Bottom line is their alcoholism finally caught up with them as they turned 40.

He was THE MAN in the 60s, what with Lawrence, Becket, The Lion in Winter among a succession of popular films. He was a major star and enormously respected actor. (To this day, Anthony Hopkins considers him the best actor he's seen). But after Ruling Class, his career fizzled. I believe he had serious health issues: he, Harris, and Burton were all totally out-of-control alcoholics. At any rate, its a shame that a talent that burned so bright should have sputtered into once was status so relatively young.
It's interesting that O'Toole and Richard Burton followed more or less the same trajectory: giving amazing performances in some of the best films ever made during the 1960's, and then giving lackluster (at best) performances in mediocre (or outright terrible) films a decade later. Their alcoholism and tempers had a lot to do with it. The other aspect of it was that they were getting too old for the "leading men" roles that they were used to.

what happened to his career?
well.. I would say a lot of bad choices! professionally I must state.
the roles he chose were not grand enough, and not even art house enough.
his agent should be shot.
It was not like he was ever blacklisted from hollywood because he was unprofessional or anything, he was just picking stupid roles!
I cant believe that's all what was being offered to him.
did he even audition for parts? maybe he just got lazy and couldnt be bothered
maybe he just enjoyed partying and only did movies to fuel his lifestyle and just continued to do the theater. as that was where his passion was.
enjoying life, taking off every summer back to ireland, playing sports, drinking, hanging out, then doing a couple plays, a couple movies for the pay check and then summer all over again etc etc maybe he r238eally didn't care all that much.
by the time the 80's came and he was into his 50's I guess he knew he was hanging onto his old star, everyone now and then a great part would come up.
but very rarely, BUT WHY! seems, michael caine, bob hoskins, alec guiness, edward fox, anthony hopkins, etc etc were all getting a lot of good parts and only a couple of stinkers, but seemed Peter was getting A LOT of stinkers and only one or two good ones.
ohh well.. it's not new to hollywood, many stars have shined bright then dimmed
btu peter's always shined bri5b4ght enough I guess.
he did it his way!

LOL yeah right, you know nothing of acting! have you ever seen him on stage?
NO.. Run along now and watch sly stallone now..

Sure, sure. We're all wrong and you're the Enlighted one Yawn.
beep troll.

http://mulhollandcinelog.wordpress.com/

Just an overrated old drunk, never subtle or with any depth.a loud ham adept at shouting and waving his arms. His career nosedived when everyone realised the emperor was naked.

O'Toole experienced a burnout circa 1972 and stopped acting for about a year. I think he tried farming. It might have had something to do with his alcohol addiction too and the need to get away from the partying lifestyle.
O'Toole claims he quit binge drinking in 1971.
He then returned to the stage in 1973, but good screen roles were no longer offered probably due to his reputation. He accepted Rosebud when friend Robert Mitchum pulled out and then a few more forgettable roles.
Then two illnesses in the mid-70s: operation on the pancreas and a blood disorder. Took a while for him to get back into the spotlight. He filmed The Stuntman in 1978 and it wasn't released until 1980.
I'd love to read a really thorough biography of O'Toole, because there are many interesting stories there. And I don't mean the fun drinking stories, but rather the not-so-fun reality, mixed with the triumphs.
Like the time he came on Johnny Carson in 1962 and was unable to speak because he was so drunk and the way he wept after it happened. His otherwise impressive knack for self-control in staying sober while shooting and completely wasted between projects. And that fascinating story of how Fellini came up with Toby Dammit after seeing O'Toole throw up on a waiter, subsequently offering him the said role which O'Toole turned down when he figured out it was about him.
O'Toole fascinates me. So brilliant yet so flawed, and thus relatable in a weird way, even though he's obviously a genius. Has anyone seen the clip of him and Orson Welles discussing Hamlet in 1963 on youtube? The world was at his feet.