Teen Titans is based on the DC Comics superhero team, the Teen Titans, primarily the stories told in the early-1980s The New Teen Titans comic book series by Marv Wolfman and George Pérez. The series revolves around main team members Robin (the leader), Raven, Starfire, Beast Boy, and Cyborg. While it is an action cartoon, the series is also character-driven, with a focus on the main characters' struggles with being teenage superheroes, their mutual friendships, and their limitations. A major difference between the animated series and the comic book is that while the comic portrayed the characters as being in their late teens to early 20s (resulting in the comic series at one point even dropping the word "Teen" from its title to reflect its older characters), the animated series characters are all depicted as being in their actual mid-teen years. Seasons two and four are based upon two of the most popular New Teen Titans arcs, "Judas Contract" and "Terror of Trigon" respectively. Many characters from the comics, including Aqualad, Bumblebee, and Speedy, appear throughout the series. This is especially true in the final season, which introduces many Titans from the comics into the series for the first time, as well as the Doom Patrol heroes and villains. The group's base of operations is Titans Tower, a large T-shaped structure that combines living quarters, a command center, training/workout facilities, and hangar/garage space. It sits on an island just offshore from a fictional West Coast city; the location is never stated in any episode (though geographically it seems to be based on San Francisco), but is identified as "Jump City" in the Teen Titans Go! comic series. At the end of the third season, a second team of Titans comes together in Steel City, on the East Coast, and builds a similar Tower to serve as home base. However, instead of a free-standing structure on an island, this one is set into the cliff on which the city is built. Teen Titans frequently uses self-referential humor, and its animation style is heavily influenced by anime. On different episodes, the series' theme song's lyrics alternate between English and Japanese, sung by the J-pop duo Puffy (called "Puffy AmiYumi" in the United States to distinguish it from Sean Combs). Andrea Romano revealed in an easter egg on the season 3 DVD that the Japanese theme song means it will be a silly episode, while the English theme songs means it will be a serious episode (with the exception of "Nevermore"). This can be accessed by going to the special features menu on disc 2 and selecting the + sign on Más' chest; examples are then shown.