While his talent and charisma have always been undeniable, he was long plagued by offscreen troubles that threatened to sink his career.

But over the last decade, he's experienced a personal and professional resurgence that has him on top of the world and Hollywood's A-List.

It's not easy to go from high school dropout to founding member of the Avengers, but showbiz and struggle have been in Downey's blood from the beginning.

Underground Dad

Downey's irreverence, self-deprecating humor, and anti-authoritarian streak make a lot of sense if you're familiar with his father.

Robert Downey, Sr. started writing and directing independent films in the early 1960s.

His first film to receive a wide release was the 1969 satire Putney Swope, the story of a black man accidentally put in charge of an advertising agency.

Junior made his film debut as a 5-year-old in his dad's 1970 movie Pound, in which all the actors play dogs.

"That tornado scared me so much, it made my hair disappear."

"Have any hair on your ball(s)?"

A year later, Downey, Sr. let his 6-year-old son try marijuana for the first time, which Downey Sr. later came to greatly regret.

When his parents divorced in 1978, a 13-year old Junior followed his dad from New York to L.A.

At the age of 16, he dropped out of high school to pursue acting full-time.

New York Beginnings

Rather than attempt to break into Hollywood, the teenage Downey returned to his mother's in New York.

He landed roles in a couple of small productions, including 1984's Firstborn, a little-remembered drama co-starring an 18-year-old Sarah Jessica Parker.

The two hit it off immediately, beginning a relationship that would last for years even as Downey became a mainstay on the New York party scene.

In 1985, Downey joined the cast of Saturday Night Live.

Producer Lorne Michaels had just returned to the show after five years away, and he hired an entirely new cast.

It became painfully apparent that Downey was out of his element.

"That simply represents a dramatic synthesis of the..."

Much of the new cast failed to click with each other, and Downey was among those who were canned at the end of the season.

Professional Success, Personal Troubles

The sacking from SNL was a blessing in disguise, as it coincided with the rise of Downey's film career.

He had small roles in the John Hughes films Weird Science and Pretty in Pink, as well as the Rodney Dangerfield comedy Back to School.

1987 brought two highlights: his first lead role in The Pick-Up Artist, and Less Than Zero, his most critically acclaimed performance to date.

Less Than Zero featured Downey as the hard-partying cocaine addict Julian Wells.

It earned him recognition as a serious actor, but the experience of making it had some very unfortunate repercussions.

Drugs had virtually always been a part of Downey's life, but he's pointed to Less Than Zero as the time when the troubles really began.

He explained to The Guardian:

"The character was an exaggeration of myself.

Then things changed and, in some ways, I became an exaggeration of the character.

That lasted far longer than it needed to last."

The A-List

The 1992 bio-pic Chaplin cemented Downey's reputation as a critically acclaimed actor.

His performance as screen legend Charlie Chaplin made him one of the most in-demand stars in Hollywood and earned him a Best Actor Oscar nomination.

He followed that up with acclaimed turns in Robert Altman's Short Cuts in 1993 and Oliver Stone's Natural Born Killers in 1994.

His personal life was also looking up, as he married actress Deborah Falconer in 1992, and they had a son two years later.

But his troubles with addiction would soon boil over.

Nearly Losing It All

In June 1996, Downey was arrested for felony cocaine and heroin possession after being pulled over for driving while completely naked in Malibu.

A few weeks later, an extremely confused neighbor found the actor cozily tucked into bed in one of his guest rooms.

Numerous trips to rehab seemed to do nothing to quell his habit, and his film roles diminished in size and frequency as the arrests piled up.

A brief comeback on the hit TV series Ally McBeal was derailed by more drug charges in 2001.

He appeared on The Oprah Winfrey Show in 2004 and spoke about his struggles:

"It's not that difficult to overcome these seemingly ghastly problems."

“You are saying that it's not that difficult?”

“No.

What's hard is to decide.”

Cleaning Up His Act

Downey's marriage to Falconer ended in divorce in 2004, but he had just met producer Susan Levin the year before on the set of Gothika, and things turned serious pretty quickly.

But Levin let it be known that she wouldn't marry Downey unless he gave up drugs completely.

This was the final nail in the coffin for his old life, and the two married in 2005.

With a newfound focus and sobriety came an uptick in the number of interesting roles offered to Downey.

Well-received turns in Kiss Kiss Bang Bang, Good Night and Good Luck, and A Scanner Darkly culminated in a supporting role in the 2007 thriller Zodiac, one of the most acclaimed films of that year.

The Role Of A Lifetime

2008's Iron Man has been called, in retrospect, the riskiest film in history.

By the time of its release, Marvel had been planning that all of its future films would take place in the same shared universe, with characters crossing over between films.

Iron Man set the tone for this universe, essentially selling the whole concept of the MCU to filmgoers.

Much of this depended upon its leading man, and if the film had flopped, Downey's career might have recovered, but Marvel likely never would have.

But of course, the film was a smash hit with critics and audiences alike, and among all of the praise, Downey was singled out for inhabiting his character in a way that few superhero movie leads have done before or since.

The MCU has gone on to become the highest-grossing film franchise of all time, and Downey has been its face from the very beginning.

While he's also continued to snag an Oscar nomination for 2008's Tropic Thunder and to create a popular new spin on Sherlock Holmes, it's become increasingly difficult to tell where Downey ends and Stark begins.

"The truth is...I am Iron Man."