Robert Downey Jr. doesn't want to be pigeon holed as esoteric. He'd prefer to be fundamental.

Robert Downey Jr. is considered by many in the film industry to be a Tom Cruise who can act. While his bankability at the box office isn't exactly up to that of Cruise, his performances in films like True Believer, Chances Are, Less Than Zero, 1969 and now Air America have established him as one of the few - very few - actors in Hollywood who can star in a picture, please an audience and get raves from the critics. One reviewer was moved by a Downey performance to remark, "He's a true artist in a town filled with masters of forgery."

"I have problems being called an artist. I don't have dirty fingernails and I don't live on a budget of $70 a week," says Downey, seated on an overstuffed sofa in his dramatically decorated living room, lined with pictures of his actress girlfriend Sara Jessica Parker and studded with various art deco and art nouveau pieces. Downey's multi-level house sits just above the buzzing Sunset Strip in West Hollywood. Built in Hollywood's heyday - the Twenties - it was designed by Cecil B De Mille's set decorators, and later owned by Charlie Chaplin. Downey's existence seems comfortable; serene, clean, affluent. But, like so many of Hollywood's finest actors, his life is not what it seems. He reads his state of mind as: "Today - this whole week in fact - I've not been satisfied with who I am. Maybe in two weeks I'll feel better about me. For now, I'm striving for a change." And he plays by no one's - and no company town's - rules. "The only limits on me are the ones I've set for myself. And those are few. I'm not interested in working with anyone who wants to tell me, 'Reel it in, babe, reel it in.' I'm into reeling it out."

Downey was born twenty-five years ago in New York City. At that time, his father was fast becoming one of the premiere underground filmmakers of the Sixties, making movies which were filled with social satire and controversial themes. Robert Jr. remembers, "When Putney Swope came out, Dad thought it would be wise for us all to leave the country. So me, my mom and my sister moved with him to London. I was five. Dad said he chose London because after what was going on in New York, he wanted to go somewhere really boring. "I went to Perry House School in Chelsea, at least I think it was in Chelsea," recalls Downey. "I spent half my school days there in a corner because the teachers would say, 'Robert?' And I'd say, 'What?' Then they'd say, 'Don't say "What?", say "Excuse me."' And I'd say, 'Huh?' And they'd say, 'Go and stand in the corner.' However brief, I didn't enjoy England's educational system. The teachers seemed awfully uptight."

Downey's childhood was similar to that of an army brat. He travelled almost constantly, following his father from film location to film location. After a few months of quiet in London, the Downeys headed back to New York where Downey Sr. filmed the insanely erratic satire Pound (1970), in which impounded dogs (played by humans) awaited an owner, or the big sleep. Critics raved about the film's macabre humour. It was in Pound that Downey Jr. spoke his memorable first line on screen. "My big scene was when I went up to this guy who was playing a Mexican Hairless," says Downey. "I played a puppy and I asked him, 'Got any hair on your balls?"' Downey doesn't recall his first few forays into filmmaking as pleasant experiences. "I couldn't understand why we had to shoot scenes over and over. It was disconcerting and rather boring. More boring than London had been."

His teenage years were spent shuttling between New York and Los Angeles. "Looking back on it, it truly was life in the fast lane," says Downey. "For a teenager, it was rather confusing. Always on the move, hanging out with this group here and that group there. It was during that time that I started to indulge in a variety of drugs. "Due to the drugs I was taking, I was completely inaccessible - emotionally, physically and professionally - I was not dealing with my life in an effective manner. Instead, I was creating a separate reality from the one in which I now live, and was dealing with that reality as best I could."

After voluntarily checking himself into a twenty-eight-day drug rehabilitation programme in Arizona in 1989, Downey emerged clean for the first time in his post-pubescent life. "The Eighties for me was a period about abusive behaviour and drugs. There were years where I found myself standing around in crowded clubs looking for 'happiness' - whatever that was. I'd wake up in a dorm room at NYU and not know who or how - 'Oh, it's Brian. Oh, yeah, right' - you know, piecing your previous night back together. After a year or so, you start to realize you're not dealing with your life. You're living it, but you're not dealing with anything. My life was filled with pot and coke and theme parties. The things I remember from that period are rental cars, flying back and forth, doing Saturday Night Live (Downey was one of the regulars in the later series), partying - a lot of partying, with everyone and anyone. It was madness. Pure madness."

Downey's zombielike existence in the Me decade was mirrored by a character he played in 1987's Less Than Zero. The movie examined adolescent life in LA's fast lane. Downey played a young man who supported his freebase habit through prostitution. The film was savaged by critics, but Downey's own performance was heralded by the same reviewers as "brilliant". "Less Than Zero was a strange experience for me," says Downey. "It's probably my best performance. It's the closest I've ever come to leaving a part of myself up there onscreen for people to look at and examine. The part was relevant to what I was going through in my personal life at the time. I consider myself lucky to have gotten through that period with any sort of career and a working respiratory system."

Downey's drug dependence was complicated by his fear that without substances there would be less talent, less artistic intensity. "Now I realize I don't have to get drunk or high to sustain a high level of Dionysian energy - the kind of out-of-control state which I feel is a prime force of my acting. I have to be able to just let myself go, to be in a giddy, fuck-it kind of state in order to turn in a good performance," he says. 'And now, I'm doing that sober."

Downey began to appear consistently in theatres in the second half of the Eighties. It was then that his movie career began to gain momentum. Between 1986 and 1990, he worked on nine films back-to-back. He stars with Mel Gibson in his latest film, Air America (released here this month), in which the two play CIA agents working in Vietnam just before the war begins to escalate.

Air America (the name of a CIA-run 'airline' in Vietnam) was a troublesome movie for Downey to make. "It's very easy to slip into a 'one for them, one for me' mentality about your career in Hollywood," he says. "You feel you have to do the commercial films in order to keep your visibility high and your agents and managers happy, but you want to do films that are important, too. That's pretty much the way I've been running my career. But since Air America, which was one for them, I've decided that's bullshit. From now on, it's all for me."

In the end, Downey changed his view of the film, and came to see working on it as a positive experience. "The realization near the end of Air America was that my cynicism about the film was polluting my life," he says. "You know, I sat over there in Thailand, and when Sara would call, I'd talk about how bad everything was, you know, it's basically hip in our culture to be cynical. But halfway through the film, I realized that a cynical attitude keeps you in a non-learning state. I started to look at everything differently. I started to say to myself and everyone else, 'You know, things aren't that bad here."'

At first, Downey was trepidatious about meeting his costar. "How was I not to be intimidated by this guy who was so well-versed in both acting and action films?" says Downey. "When I first met him, I was detoxing from one of the seventy substances I'd been doing and my skin was a mess. When I met his family, one of his kids pointed at me and said to Mel, 'He's got the measles!' We both laughed and I knew things between us were going to be OK."

Downey's next film after Air America will be Too Much Sun. Directed by his father, it will mark something of a comeback for Robert Downey Sr. The issues dealt with in the movie - homosexuality, greed, death and deception - are typical of Downey Sr's oeuvre. In Too Much Sun, a rich man dies. His will states that only one of his two children, the one who produces an heir first, will inherit his millions. The punchline is that his son (Eric Idle) is gay and his daughter (Andrea Martin) is lesbian. Robert Jr. is cast in a supporting role. "I really enjoyed working with my father again," he says. "I think we're going to start doing a lot more together."

Downey is currently shooting Soapdish, in which he stars opposite Sally Field and Kevin Kline. The movie is a comedy revolving around actors working on a TV soap opera. Downey plays the soap's producer. While on the set his ear is to the phone, working on snagging a role he's wanted for a long time. He has been talking with Sir Richard Attenborough about starring in the director's biopic of Charlie Chaplin. "How many other actors who could do the part live in one of Chaplin's old homes?" he asks.

I gather up my things and prepare to leave, and Downey rises from the sofa and walks me to the door. "When you listen to the tapes, call and let me know if anything sounds really awful," he says. "I'm in this period right now where I'm just starting to do interviews again. I want to be careful about to whom I talk and about what I say. Maybe I'm being paranoid, but I don't want to be pegged - to be nailed as esoteric. What I feel I'm being is fundamental. That is, everything I've talked about today centres around fundamental truths; at least for me they're fundamental truths. But, come to think of it, in two weeks they may not be. I'll have changed again by then. Maybe you'd better schedule me for an interview every two weeks until you're ready to write this story. Otherwise, you won't be getting me right. You'll be getting someone I used to be, someone I'm not anymore."

"Robert," I say, heading down the steps to the street, "I don't think either of us has that much time." "I guess you're right," he says, waves, and closes the door.