During the Bronze Age of Comic Books, writer Marv Wolfman became popular among DC's readers for his work on "Weird War Tales" and "The New Teen Titans". George Pérez, who illustrated "The New Teen Titans", also began to rise to prominence in this era. In 1984, Pérez entered into an exclusive contract with DC, which was later extended one year. Although "The New Teen Titans" was a major success for DC, the company's comic book sales were still below Marvel's. Wolfman began to attribute this to the DC Multiverse, feeling "The Flash of Two Worlds" had created a "nightmare": it was not reader-friendly for new readers to be able to keep track of and writers struggled with the continuity errors it caused. In "The New Teen Titans" #21 (July 1982), Wolfman introduced a new character: the shadowy, potentially villainous Monitor; this laid the foundation for "Crisis on Infinite Earths".