issue, the Hulk left once he realized how much the others feared his unstable personality. Captain America joined the team in issue #4 (March 1964), and he was given "founding member" status in the Hulk's place. The Hulk, upset about being replaced by Captain America and the apparent betrayal by Rick, sought revenge against the Avengers, who teamed up with the Fantastic Four to stop him in The Fantastic Four #26 (May 1964). The Avengers went on to fight foes such as Baron Zemo, who formed the Masters of Evil, Kang the Conqueror, Wonder Man, and Count Nefaria. The next milestone came when every member but Captain America resigned; they were replaced by three former villains: Hawkeye and the Maximoff twins, Scarlet Witch and Quicksilver. Giant-Man, now calling himself Goliath, and the Wasp rejoined. Hercules became part of the team, while the Black Knight and the Black Widow abetted the Avengers but did not become members until years later. Spider-Man was offered membership but did not join the group. The Black Panther joined after rescuing the team from the Grim Reaper and Klaw. The X-Men #45 (June 1968) featured a crossover with The Avengers #53 (June 1968). This was followed by the introduction of the android Vision. Pym assumed the new identity of Yellowjacket in issue #59, and married the Wasp the following month. The Avengers headquarters was in a New York City building called Avengers Mansion, courtesy of Tony Stark (Iron Man's real identity). The mansion was serviced by Edwin Jarvis, the Avengers' faithful butler, and furnished with state of the art technology and defense systems, and included the Avengers' primary mode of transport: the five-engine Quinjet. The prequel comic Avengers #1 1/2 (Dec. 1999), by writer Roger Stern and artist Bruce Timm, told a retro-style story taking place between issues #1 and #2, detailing Ant-Man's decision to transform himself into Giant-Man. 1970s The team encountered new characters such as Arkon in issue #75 (April 1970) and Red Wolf in #80 (Sept. 1970). The team's adventures increased in scope as the team crossed into an alternate dimension and battled the Squadron Supreme, and fought in the Kree-Skrull War, an epic battle between the alien Kree and Skrull races and guest-starred the Kree hero, Captain Marvel. The Avengers briefly disband when Skrulls impersonating Captain America, Thor, and Iron Man used their authority as founders of the team and disbanded it.