In the two Tribble episode (TOS and DS9) we see the Klingons as looking very different to the ridged aliens we know and love.
When Worf was asked about this he didn’t really give any info.
Have the ST people tried to come up with anything to cover this difference which was forced upon them because of the TOS’s depiction of Klingons?
Nope. That was the only reference to it. I’ve read some possible, humourous explanations of it. Nothing solid, though.
Worf simply stated that Klingons didn’t like to talk about it.
The closes thing to an official explanation was made by the editor of the Star Trek paperbacks, John Ordover.
He said the Klingons always had ridges, but that television transmission in the 1960s was too primitive to pick them up.
Of course, Ordover also explained the reason why the outside temperature in one ST episode was below absolute zero was due to the wind chill factor.
He also was behind “Kirk and Tasha in Love” . . . Hmmmn.
Thanks beatle. Don’t know how I missed that thread.
Mod.s there doesn’t seem to be a definate answer and there’s already a thread about this so you can do what you will with this. 
One of the leading theories is that the Klingons made extensive use of genetic engineering to make them tougher and more effective as warriors. This theory has some circumstantial evidence to support it. Remember, Kirk could beat up a Klingon in hand-to-hand combat. Who on TNG or DS9 could possibly kick Worf’s ass?
An alternate theory draws a parallel to America’s Indian Wars in the 1800’s. By this theory, the Klingons in TOS are a different race/ethnicity than the Klingons in TNG and later series. The latter group of Klingons overthrew the former sometime between TOS and TNG, but they did so in a very dishonerable way, so they don’t like to talk about it.
Oh my God, I really am a Star Trek geek :eek:
Who could kick Worf’s ass in TNG?
Data. (maybe unfair answer)
IIRC, the Star Trek RPG explained TNG-looking Klingons as “purebreds” and TOS-looking Klingons as Human-Klingon mixes (akin to Spock being a Human-Vulcan mix). For what it’s worth…
Seems like in the beginning of TNG, no one except data could. Then, later in the series, it seemed like every new alien had to prove their toughness by beating up Worf.
The Star Trek comics explained it by saying there were two races of Klingons, the smooth-browed and the ridge-browed. At the time of Capt. Kirk, the smooth-browed Klingons were in power. Sometime later, they were overthrown and the ridged-brow Klingons came into power. They then sent all the smooth-browed Klingons out into space to serve on out of the way Klingon outposts.
Unfortunately, ST-Deep Space Nine shot a hole in this story by bringing back three Klingons from the TOS era, and portraying them with ridged-brows. There is some fannish discussion that the Klingons induldged in genetic engineering or plastic surgery, but this is not canon (and doesn’t really fit in with the total Klingon philosophy). In short, nobody knows.