Claremont launched various "X-Men" spin-offs, beginning with "The New Mutants" in 1982. The spinoffs "Excalibur" and "Wolverine", initially written by Claremont, followed in 1987 and 1988, respectively. "X-Men" crossover stories written by Claremont during the latter half of his tenure on the series include "Mutant Massacre", "Fall of the Mutants", and "X-Tinction Agenda". In 1991, Marvel launched a second "X-Men" title simply called "" with Claremont and penciler Jim Lee as co-writers. "X-Men" #1 is still the best-selling comic book of all-time, with sales of over 8.1 million copies (and nearly $7 million), according to "Guinness World Records", which presented honors to Claremont at the 2010 San Diego Comic-Con. The sales figures were generated in part by publishing the issue with four different variant covers which showed different characters from the book (and later a fifth gatefold cover that combined all four), large numbers of which were purchased by retailers, who anticipated fans and speculators who would buy multiple copies in order to acquire a complete collection of the covers. Claremont left the series after the first three-issue story arc, due to clashes with editor Bob Harras.