X-Force, featuring the characters from The New Mutants, led by Cable; it was written by Rob Liefeld and Fabian Nicieza. Internal friction soon split the X-books' creative teams. In a controversial move, X-Men editor Bob Harras sided with Lee (and Uncanny X-Men artist Whilce Portacio) over Claremont in a dispute over plotting. Claremont left after only three issues of X-Men, ending his 16-year run as X-Men writer. Marvel replaced Claremont briefly with John Byrne, who scripted both books for a few issues. Byrne was then replaced by Nicieza and Scott Lobdell, who would take over the majority of writing duties for the X-Men until Lee's own departure months later when he and several other popular artists (including former X-title artists Liefeld, Portacio, and Marc Silvestri) would leave Marvel to form Image Comics. Jim Lee's X-Men designs would be the basis for much of the X-Men animated series and action figure line as well as several Capcom video games. The 1990s saw an even greater number of X-books with numerous ongoing series and miniseries running concurrently. X-book crossovers continued to run annually, with "The X-Tinction Agenda" in 1990, "The Muir Island Saga" in 1991, "X-Cutioner's Song" in 1992, "Fatal Attractions" in 1993, "Phalanx Covenant" in 1994, "Legion Quest"/"Age of Apocalypse" in 1995, "Onslaught" in 1996, "Operation: Zero Tolerance" in 1997, "Hunt for Xavier" in 1998, "The Magneto War" in 1999, "Apocalypse: The Twelve" / "Ages of Apocalypse" in 2000 and "Eve of Destruction" in 2001. Though the frequent crossovers were criticized by fans as well as editorial and creative staff for being artificially regular, disruptive to the direction of the individual series, and having far less lasting impact than promised, they continued to be financially successful. There were many additions to the X-Men in the 1990s, including Gambit, Cable, and Bishop. Gambit became one of the most popular X-Men, rivaling even Wolverine in size of fanbase after his debut in Uncanny X-Men #266 (Aug. 1990). Many of the later additions to the team came and went, such as Joseph, Maggott, Marrow, Cecilia Reyes, and a new Thunderbird. Xavier's New Mutants grew up and became X-Force, and the next generation of students began with Generation X, featuring Jubilee and other teenage mutants led and schooled by Banshee and ex-villainess Emma Frost at her Massachusetts Academy. In 1998, Excalibur and X-Factor ended and the latter was replaced with Mutant X, starring Havok stranded