The 1997 film "Titanic" turned the actor into a global star and Leonardo admits he struggled to cope with his newfound fame.
Leonardo, 31, told Britain's Independent newspaper: "As soon as people give you compliments and you suddenly have more power than you've ever had in your entire life, it's not so much you become an arrogant p***k, but you get a false sense of your own importance."
"You're treading on dangerous territory when you begin thinking you've actually altered the course of history."
Though he starred in several films before "Titanic," Leonardo rocketed to fame playing Jack Dawson in the movie which still holds the box-office record for the biggest grossing film of all time.
The "Gangs of New York" actor admits fame happened too fast for him to handle.
He said: "Everything happened so quickly. I began to feel engulfed by it."