Unknown is a relative term- it can apply to somebody who has film credits, but isn’t exactly a name everybody would know.
Two of my pics:
Hayden Christensen in STAR WARS 2 & 3 (I actually thought of this thread while watching the Star Wars trailer). He is pretty but painful to watch, though I don’t think acting talent has ever been a major consideration of Lucas’s (why he signed Alec Guinness rather than Tom Bosley, who I’m sure would have been cheaper, is beyond me).
Diana Scarwid in Mommie Dearest- were ostracism still practiced I’m pretty sure she’d have had to learn Greek and take up residence on a tiny Aegean island. Admittedly it’s probably difficult to give a dramatic performance when you’re alongside CAMP DUNAWAY and you’re dressed like Dainty June from Gypsy, but even so her underacting would have been enough evidence to get a feeding tube pulled in 32 states.
Diana Scarwid already had an Oscar nomination in her belt by the time Mommie Dearest was released, so I wouldn’t necessarily call her unknown. Maybe not a household name, but few movie actors generally are (and MD wasn’t a particularly Big movie either, just notorious).
Instead of choosing a famous (or even semi-famous) American actress like the studio wanted, Michael Cimino drew a line in the sand over Isabelle Huppert (who was virtually unknown outside of France) when casting Heaven’s Gate. She’s genuinely talented, but all-wrong for a film that had plenty wrong already going against it anyway.
Doesn’t the all-time champ in this department have to be Klinton Spilsbury in 1981’s The Legend of the Lone Ranger? He never acted before, and he never acted again!
Sofia Coppola in The Godfather III was unknown and horrible.
And the little kid who played the young Anakin in Star Wars Episode I: The Erotic Adventures of Jar-Jar was also dreadful, although I think Lucas can make any actor seem dreadful so I feel bad for the kid.
No one should be judged solely by their acting while directed by George Lucas. He’s excellent in Shattered Glass, and received a GG nomination for Life as a House.
Maybe it’s the DNA, but this was my first thought as well when I read the OP. Even Ms. Coppola had a few credits before The Godfather III, even when you don’t count her father’s works.
I thought that Jake Lloyd, who played young Anakin Skywalker in “Star Wars: Episode I,” was a charmless, wooden, infuriatingly dull actor. Surely George Lucas could have found a better child actor for this important role. If someone of the caliber of Haley Joel Osment had been cast as Anakin, this would have been a much better movie.
Which to me has always begged the question, why the hell did they cast him? How can you not know that somebody has a voice so wrong for the part it will have to be redubbed, or that he can’t act for beans, during the audition process?
The main thing I remember about the time that movie came out was that Clayton Moore was ordered in court to stop wearing his Lone Ranger mask at public appearances (which I would imagine was his primary source of income at the time- I don’t know that). He made lemonade by becoming the celebrity spokesmodel for a line of designer sunglasses that he substituted, but eventually (once the movie tanked) resumed wearing the mask.
Not entirely unknown then, but pretty painful to watch now. Although I must admit I was mesmerised by his portrayal at the time it came out. But, I was also starting into body building at the time and was just a dumb teenager.
Berkeley was reasonably famous; I knew who she was, and I’d never seen a single minute of “Saved by the Bell.”
Bryan, Christopher Reeve was GREAT in Superman.
My choice would have to be Sofia Coppola. Look, I’ve seen both “Godfather III” and “Attack of the Clones,” and compared to Sofia, Hayden Christensen looked like Sir Alec Guinness. Her performance was as bad as any I’ve ever seen in an honest-to-God theatrical release.
The only worse actors I’ve ever seen are either people who got movie roles by being good at something else (Steven Seagal, Ice-T) or, in one individual case, the worst actress who ever lived: Rebecca Pidgeon.
James Toback who has claims as the worst director to make movies regularly came out with Black & White in 1999. Toback brilliantly had the non-actors in his cast improvise many of their scenes. There are too many duds to list them all but you haven’t seen bad acting until you see improvised bad acting. Admittedly only $10,000,000 was wasted making it.