Asked if he was ever tempted to go over the top in making this character evil, Williams told United Press International: "No. Not at all."
"There was no need to... There was never a temptation. Plus, it was Al, as in 'Pacino.' He said, (Williams does a perfect Pacino imitation,) 'Don't do that' and (director) Christopher Nolan knew exactly what he wanted... There was an ease about this that I've only had once before with ('Good Will Hunting' director) Gus Van Sant where you get so relaxed. Even though you're doing this intense stuff, you just feel at ease. There's no need to riff."
In this film, Williams plays an Alaska crime novelist who beats a teenaged fan to death. Pacino is the veteran Los Angeles detective sent to help Hilary Swank ("Boys Don't Cry") and her fellow inexperienced, small-town cops catch him. The title refers to the sleepless condition Pacino suffers when faced with the northern town's nearly constant daylight -- a state of being that repeatedly compromises his judgment.
Talking about his own bouts with insomnia, Williams admitted that most of his sleepless nights took place in the 1980s and could be attributed to his well-documented drug use.
"It was usually the Peruvian college fund that helped me and I was awake and there were ninjas outside my window, which was one of the reasons why I couldn't sleep. I lived in a ground-floor apartment. There was that kind of insomnia. The other type of insomnia that's not induced by chemicals is the insomnia where you go back over things that didn't go well -- like being on the Academy Awards and wearing mouse ears," he said.
Despite the fact that he has himself earned four Academy Award nominations since 1987, Williams confessed to feeling star-struck when acting opposite Pacino, the legend famous for his outstanding performances in "The Godfather," "Dog Day Afternoon," "Serpico" and "Scarface."
"When you hang out with these guys like Pacino, for me, I'm in awe," Williams said. "I stand off like everyone else, 'It's Michael Corleone,' (starts humming the theme to 'The Godfather,') and you meet them and then you get to know them."
Williams said he was thrilled Pacino lived up to his reputation as consummate professional, but added that he was equally happy to learn his hero was "really funny" and "just a sweet, kind man."
"You find out the same thing about (Robert) DeNiro," Williams said of his "Awakenings" co-star. "They're tough. They've got this hard-core reputation, but they're also very, very intelligent people, who are really well-read and also very gentle in their own way and that, to me, was a great lesson."
Williams seemed genuinely pleased to hear Pacino was just as complimentary when talking about him.
"(Williams) is my idol," Pacino told a packed press conference. "I just love being around him. I'd like to see him personally after the picture. He's a very bright, caring guy -- about the world, about everything around him. And talking to him. He's very well-informed, and he's funny to be around because he's also so sensitive, so he treats you well. I can't say enough about him and as far as funny goes, he's up there. I just recently saw his (new stand-up act.) Did you catch his act? His new thing? It's amazing. He's just amazing."
Nolan, the director of "Insomnia" and last year's critical darling "Memento," said he hired Williams because he thought he and Pacino would balance each other out in the film.
"As the story progresses, we wanted to have two larger-than-life characters confront each other in this twisted psychological cat-and-mouse game. When I met Robin and realized how clearly he understood Finch, it was very exciting to know that he was going to fit this character like a glove," Nolan said.
That "cat-and-mouse game" was one of the elements that most appealed to Williams when he read the script.
"It is back and forth," he said. "He does this, you top that. He comes back at you with another thing, playing this deadly game, back and forth until the final point."
Told he made a very good creepy, bad guy, Williams beamed and said he takes that as a compliment.
"That's great. That's lovely!" he exclaimed. "After we showed 'One-Hour Photo' at (the) Sundance (Film Festival,) a woman came up to me and said, 'That was creepy in a good way.' Thank you ... That's the purpose of a movie like this, if you find people drawn to the frightening normalcy of this character and the kind of seductiveness of trying to get (Pacino's troubled cop character) to understand and the more unraveled he is, the more empowered I am. There's a real interesting dynamic and negotiation with him and blackmailing him and giving him evidence, saying: 'You don't understand' and then, finally, at the end, unleashing the brutality of it."
Williams' role in "Insomnia" is the third dark character he has played after years of portraying warm and fuzzy good guys, who triumph over adversity.
"I just want to do characters now," Williams announced. "You hit 50 and you're heading towards Walter Brennan territory. (Assumes Walter Brennan voice) 'Look ahead! Don't go in there!' You start finding characters and it's not that idea where I'm doing a movie and I look fabulous. I don't look fabulous. Your hair starts growing out your nose and leaving your head. I'm a Chia pet. So, this is a time where I'm going to play characters now."
Williams said that he is proud of his recent streak of performances as bad guys, but admitted he would much rather his own children watch him in kid-friendly movies like "Hook" and "Mrs. Doubtfire."
"My 19-year-old saw ('Insomnia')... and he said, 'That was really good work,' which is great coming from a 19-year-old. The little ones, no, I wouldn't let them see this... They get very disturbed when they see ... Number one, when you die in a movie and especially dying this violently."
So, does the man who added the phrase "Nanoo-Nanoo" to the American lexicon during his days as an alien on the 1970s sit-coms "Happy Days" and "Mork and Mindy" feel older and wiser now that he's 51?
"The great thing about turning 50 is that you're like a good stilt -- you mature and you also smell," Williams joked. "But, the good thing is that you come with a whole different knowledge. You arrive at that conclusion where you're at a place where you're comfortable with yourself. You have to be because if you're uncomfortable with yourself at 50, uh-oh. Then you start having Botox parties and looking like you've had a slight stroke, but you have no wrinkles."
Voted "Most Humorous" and "Least Likely to Succeed" at his California high school, Williams went on to nab Academy Award nominations for his performances in "Good Morning Vietnam," "Dead Poet's Society" and "The Fisher King." His fourth nomination earned him an Oscar for his portrayal of compassionate and intelligent counselor Sean McGuire in "Good Will Hunting." Seen earlier this year in Danny DeVito's dark comedy, "Death to Smoochy," he also appears in the film, "One-Hour Photo," due out this summer. His most recent stand-up routine will also appear as an HBO special this July.