Would Nikola Tesla count? His contributions to science are unquestioned but he had some really out-there ideas, especially later on in life.
I think he’s pretty much the archetype of “bleeding edge scientist becomes obviously crazy crank.”
Jeff Meldrum is a professor of anatomy and anthropology at Idaho State University. Not dean of Harvard, but nothing to sneeze at either.
His main research area is Bigfoot, in whose existence he passionately believes:
That’s correct. 
Hoyle was the second person I thought of. The first, though, was Mordehai Milgrom, who’s long been pushing the hypothesis that there is no dark matter, and that instead gravity itself is modified in some way. The problem is that his Modified Newtonian Gravity can’t fit all of the many different dark matter observations at once, it’s very difficult to make it even self-consistent, and nobody has ever even proposed a relativistic form of the model. It may be that he’s stumbled upon some interesting emergent phenomenon in dark matter distributions in galaxies, but it’s obscured behind his mountains of nonsense.
This example doesn’t fit neatly into the OP’s requirements, but it’s an interesting story. Zoology blogger Darren Naish describes it as “taxonomic vandalism.” Here’s his post on the issue.
The particular idiot in question is an amateur herpetologist, who, for his own bizarre reasons, has taken it upon himself to rename and reclassify Australian reptile fauna. He has succeeded in publishing a LOT of papers, by dint of founding his own “journal.” Because of the ICZN’s established rules of taxonomy, including the Principle of Priority, the ludicrous new names he applies are, technically, valid.
The guy (I’m not using his name, as he probably has Google alerts up the wazoo and is loudly defensive of his “work”) is also known as a cowboy snake exhibit, draping venomous snakes, that he has surgically altered, all over children. He gives me the heebie-jeebies. I really wish he would stop.
Some examples no one’s mentioned yet:
Halton Arp, an astronomer who disagreed with the Big Bang. He thought quasars were associated with relatively nearby galaxies, rather than being extremely distant phenomena.
More Big Bang non-agreers were Geoffrey and Margaret Burbidge.
In geology, Samuel Carey advocated that plate techtonics was driven by the Earth expanding rather than subduction.
John Christy, climate change denier. One of the few competent, intelligent climate scientists who do so.
There are tons of examples in the ever-popular and lucrative field of climate change denial, literally far too many to list. But one of the more notorious ones was the physicist Frederick Seitz, who was among other things the recipient of the National Medal of Science and was the president of Rockefeller University and, incredibly, was for a time president of the National Academy of Sciences. He was also pathologically dishonest and had all the integrity of a sewer rat, first contracting with R.J. Reynolds to lend his credentials to undermining the science about the dangers of tobacco, then launching an all-out attack on climate science.
Seitz was one of the key principals behind the disreputable Oregon Petition in which a large number of scientists allegedly questioned the reality of climate change, wherein it turned out many of the names were completely fabricated and the rest either worked in completely unrelated fields or else had their views misrepresented. The Oregon Petition was accompanied by a 12-page article questioning climate change that looked exactly like a paper from the Proceedings of the National Academy of Sciences, which turned out to be a forgery created by Seitz and which precipitated an extraordinary public reprimand from the NAS.
There are also a very small number of real scientists working in the field of climate science who knowingly publish garbage. Willie Soon and Sallie Baliunas are two names often found together in this context. Roy Spencer is another, a name almost invariably found on the Internet as “Roy Spencer, Ph.D.” to make it clear what you’re dealing with when you deal with Roy. Spencer is simply a far-right political ideologue misappropriating and distorting science for political objectives. Steve McIntyre and Ross McKitrick are another dynamic duo particularly noteworthy for their incessant attacks on the distinguished climate scientist Michael Mann. McKitrick is actually a mining engineer but McIntyre is an academic mathematician, and the duo published a paper making some minor but ultimately irrelevant criticisms of some of Mann’s statistical methods. McIntyre has been beating that same dead horse on his Internet blog ever since, and complaining that no one wants to publish his brilliant observations any more.
Another interesting one is Richard Lindzen, among the more prestigious of the quacks because he was actually a reputable atmospheric physicist at MIT until his retirement a few years ago. His modus operandi was simple, and was basically modeled on Dr. Jekyll and Mr. Hyde. In the scientific domain he would publish (usually) reputable research, but his public persona was that of a staunch denialist. He would say things in public speeches and op-eds in papers like the Wall Street Journal that were scientifically laughable, but because he had a long string of legitimate publications and was a well-known academic – at MIT, no less – his words were perceived by many to carry a credibility that had absolutely no justification.
Freeman Dyson is in a different category entirely. He was a brilliant physicist who is now extremely elderly and, apparently, rather senile, and has somehow persuaded himself that climate models are inherently flawed and that, by extension, everything we think we know about the future of climate is wrong. There are actually a number of these individuals suffering some form of dementia peddling similar nonsense, but Dyson is perhaps among the most storied.
It seems to me that the Seitz and the Lindzen types, actual scientists who cynically and dishonestly abused their reputations to promote falsehoods, are the most dangerous of the quacks because they not only mislead the public but put science itself into disrepute.
How about Steve Jones, the physics professor at BYU who got involved in 9/11 conspiracies and got a few papers about thermite being used in the “demolition” of the World Trade Centers published in peer reviewed journals? I believe he had some claims about measuring the weight of souls before then, but I’m pretty sure they weren’t published in peer-reviewed journals.
The minute you said ‘herpetologist’ I was pretty sure I knew who you were talking about - and looking at your link, I was right. Dude in question used to bring his snake show to our local primary school for maybe as much as a decade - and I must say, the presenters (not him personally, but people he’d trained) were extremely professional and competent every time, and I’m not aware of anyone having any problems with the show ever.
We also had them for the Taller Girl’s birthday party, and I did research him online prior to allowing that, and discovered the loopiness, but decided that it probably didn’t detract from the fact that he runs his displays competently - and in the event, that seemed to be true.
It seems to be a case of “smart, but not as smart as he THINKS he is” syndrome
Hmmm…Dean Kenyon might qualify on the outskirts. He came to his Young Earth Creationism a decade after he was already an established biology professor ( granted not a particularly notable one ) and YEC is about as far out in crank land as it gets for most professional biologists.
These two were disrespected for some period of time: Helicobacter pylori, previously Campylobacter pylori, is a gram-negative, microaerophilic bacterium found usually in the stomach. It was identified in 1982 by Australian scientists Barry Marshall and Robin Warren, who found that it was present in a person with chronic gastritis and gastric ulcers, conditions not previously believed to have a microbial cause. I
Peter Duesberg (known for denying that HIV causes AIDS) is actually not representative of what the OP is asking about.
Duesberg has been a co-author on a fair number of research papers in recent years in decent journals, but based on a PubMed search, these are articles about genetics and carcinogenesis, not his crank beliefs about HIV. The only papers I can find regarding his HIV-doesn’t-cause-AIDS thesis since 2003 were published in the Italian Journal of Anatomy and Embryology (not exactly a high-impact publication) and Medical Hypotheses (pretty much a junk journal that accepts a lot of [del]goofball[/del] provocative ideas).
Not a good example at all.
Marshall et al’s proposition that H. pylori caused ulcers caused initial skepticism among many physicians/scientists, but followup work confirming their findings came out in fairly short order, so they were never consigned to the status of cranks like others mentioned in this thread.
http://www.csicop.org/si/show/bacteria_ulcers_and_ostracism_h._pylori_and_the_making_of_a_myth
These astrophysicists could be considered somewhat “alternative”.
Thomas Gold?
I have to agree on Penrose. Not just his ideas on consciousness, which cannot be refuted, but his claim that humans can solve problems that computers cannot, which is easy to refute. And he won’t admit he is wrong.
Another example was Linus Pauling, double nobelist, who went off the deep end over vitamin C. I don’t agree that Wakefield is an example. Total fraud.
In another era Newton spent a lot of time trying to turn lead into gold.
I believe he was rather trying to turn iron into copper (useful for casting bronze cannons). And this was hardly crank or even fringe science in an age before Dalton and the atomic theory.
You know what, I’m going to stick my neck out and suggest that pretty much every single bloody reply in this entire thread fails the OP’s criteria. Every single last one of you.
Now I’ll start by emphasising that I’m probably the Dope’s fiercest adovcate that science is an utterly human activity. Just because something is scientific doesn’t make it special. It’s just as human as anything else.
So let’s go. I’m skipping most of the humanities/biological suggestions and only a couple of the physical science ones.
[ul]Plate tectonics The arguments around mechanisms were utterly significant in the first half of the 20th century. But you then become in danger of ruling out Arthur Holmes as a mere crank. By all accounts he was always regarded as a major figure and was central to the determination of the age of the earth, several decades before plate tectonics became accepted. Not to mention his influential textbook.[/ul]
[ul]String theory Yes, controversial amongst quantum field theorists (including myself), but not obviously pseudoscience. On the whole, sensible - if highly speculative - stuff.[/ul]
[ul]Roger Penrose Kind of an example, but not terribly significant. Major figure in mathematical physics, but his stuff on conciousness is marginal. The latter got high profile publications initially, but these days? His other stuff gets paid attention to.[/ul]
[ul]Roger Stritmatter Does anybody serious take him at all seriously? Other than the fellow cranks?[/ul]
[ul]Linus Pauling How successful was Pauling in getting his Vitamin C stuff into the serious literature? And I speak as someone who once
spent an afternoon in one of the US’s main medical libraries checking whether Pauling intervened in my mother’s death from cancer. (He didn’t, but it was a minor matter of timing, rather than geography. I don’t hold the connection against him.) From memory, Pauling either had other’s lead on the key studies or he had stuff published in the Proceedings of the National Academy of Sciences. Which is a kind of bias in these matters: elected Fellows get to publish, or recommend, stuff without peer review. So rubbish endorsed by elderly, but eminent, cranks gets published in high profile journals.[/ul]
[ul]James Lovelock As noted, a bit of an odd case.[/ul]
[ul]Pons and Fleischmann Plus Jones, of course. Cold fusion was almost correctly universally regarded as absolute nonsense from the start. From memory, Jones got published in Nature, almost entirely as a curiosity. And, again from memory, was instantly dismissed as such. Pons and Fleischmann did get published in a specialist electrochemical journal. Regarded by physicists as chemists circling the wagons unconvincingly.[/ul]
[ul]Fred Hoyle Massively emminent astrophysicist, while also generating any number of silly speculative ideas. But did any of the latter really
infiltrate the professional journals? To some extent, I’d guess, but his major noncoventional stuff was utterly via his popular books.[/ul]
[ul]Eric Laithwaite The Royal Institution Christmas Lectures are what everybody refers to. Surely minimal impact otherwise. And unconvincing.[/ul]
[ul]Stephen Jay Gould I agree with Colibri that this is just generally silly.[/ul]
[ul]Andrew Wakefield As noted, surely not being published anywhere sensible.[/ul]
[ul]Peter Duesberg A sensible track record at one time. Not remotely regarded as sensible for some time.[/ul]
[ul]Lord Kelvin and the age of the earth Lord Kelvin was not an idiot. The whole debate is rather more complicated than anybody who has read
on the details will assume.[/ul]
[ul]Kary Mullis A weirdo, while still undoubtedly deserving of his Nobel. Not sure there’s much else to say on the matter in hand.[/ul]
[ul]Lenard and Stark Evil Nazis. Their genuine contributions to physics are indeed probably somewhat overlooked as a result. Kind of difficult to big them up on that basis.[/ul]
[ul]Shockley I’ve previously discussed him.[/ul]
[ul]Lysenko A genuine candidate, in that, while utterly nuts and without merit, some contemporaries may have considered him serious, given the political conditions.[/ul]
[ul]Mordehai Milgrom I seriously don’t agree, but I’m not sure I’d consider him a crank, as such. [/ul]
[ul]Halton Arp Long before his death, surely supposedly the poster boy for the astronomer being denied access to the usual telescopes and journals. Personally - as someone
who’d read his stuff - I felt that entirely justified. But, no, he wasn’t the crank getting published.[/ul]
[ul]The Burbidges Were they actually being treated as particulary crankish? Very out there, certainly, but univerally regarded as having done good stuff in their time.[/ul]
No true crank scientist…?