He was subsequently cast as the title role in director Mark Rydell's 2001 TV biographical film James Dean.To immerse himself in the role, Franco went from being a non-smoker to smoking two packs of cigarettes a day, dyed his dark brown hair blond, and learned to ride a motorcycle as well as play guitar and the bongos.To have a greater understanding of Dean, Franco spent hours with two of Dean's associates. Other research included reading books on Dean and studying his movies. While filming James Dean, the actor, to get into character, cut off communication with his family and friends, as well as his then-girlfriend. "It was a very lonely existence," he notes. "If I wasn't on a set, I was watching James Dean. That was my whole thinking. James Dean. James Dean."Despite already being a fan of Dean, Franco feared he might be typecast if he'd captured the actor too convincingly. Ken Tucker ofEntertainment Weekly wrote: "Franco could have walked through the role and done a passable Dean, but instead gets under the skin of this insecure, rootless young man." He received aGolden Globe Award and nominations for an Emmy Award and a Screen Actors Guild Award (SAG).

2002–2007

Franco achieved worldwide fame and attention in the 2002 superhero film Spider-Man, when he played Harry Osborn, the son of the villainous Green Goblin (Willem Dafoe) and best friend of the title character (Tobey Maguire). Originally, Franco was considered for the lead role of Spider-Man/Peter Parker in the film,though the lead went to Maguire. Todd McCarthy ofVariety noted that there are "good moments" between Maguire and Franco in the film.Spider-Man was a commercial and critical success.The movie grossed $114 million during its opening weekend in North America and went on to earn $822 million worldwide.He next starred in Sonny, a 2002 release in which he was directed by fellow actor Nicolas Cage, whose involvement had attracted Franco to the film.Set in 1980s New Orleans, Sonny follows the titular character (Franco) returning home after just being discharged from the Army. To prepare for his role, he met with sex workers or people who had previously been prostitutes.The movie was panned by critics, with the New York Post's Lou Lumenick calling it an "instant candidate for worst movie of the year." Franco was cast as a homeless drug addict in the drama City by the Sea (2002) after co-star Robert De Niro saw a snippet of his work inJames Dean. He lived on the streets for several days to better understand the subject matteras well as talk to former or still using drug addicts. He also co-starred with Neve Campbell in Robert Altman's ballet movie The Company (2003). The success of the first Spider-Man film led Franco to reprise the role in the 2004 sequel, Spider-Man 2. The movie was well received by critics, and it proved to be a big financial success, setting a new opening weekend box office record for North America. With revenue of $783 million worldwide, it became the second highest-grossing film in 2004.The following year he made and starred in the black comedy The Apeand the 2005 war film The Great Raid, in which he portrayed Robert Prince, a captain in the United States Army's elite Sixth Ranger Battalion. In 2006, Franco co-starred with Tyrese Gibson in Annapolis and played legendary hero Tristan in Tristan & Isolde, a period piece dramatization of the Tristan and Iseult story also starring British actress Sophia Myles. For the former, he did eight months of boxing training and for the latter, he practiced horseback riding and sword fighting. He then completed training for his Private Pilot Licence in preparation for his role inFlyboys, which was released in September 2006; the same month, Franco appeared briefly in The Wicker Man, the remake of the seminal horror film. Also in 2006, he made a cameo appearance in the romantic comedy The Holiday.

He again played Harry Osborn in Spider-Man 3 (2007). In contrast to the previous two films' positive reviews, Spider-Man 3 was met with a mixed reception by critics. Nonetheless, with a total worldwide gross of $891 million, it stands as the most successful film in the series, and Franco's highest-grossing film to date. In this same year, Franco made a cameo appearance as himself in the Apatow-directed comedy Knocked Up, which starred Freaks and Geeks alumni Seth Rogen, Jason Segel and Martin Starr. Franco co-starred with Sienna Miller in the low-budget independent film Camille, a dark fantasy dramedy about a young newlywed couple and Interview, where he appears in a voice only role, both 2007 movies that were ignored by audiences and critics alike. Among his other 2007 projects were Good Time Max, which Franco wrote, directed and starred in. The movie premiered at the 2007 Tribeca Film Festival and centers around two talented brothers who take very diverse paths in life, one going on to become a doctor whilst the other sibling (Franco) experiences unemployment and uses drugs. The actor chose to cast himself in that role because, "It was really just a process of elimination. I was better suited for this role than the responsible surgeon."