In his original run with WWF, X-Pac was known as The 1-2-3 Kid or simply The Kid. The only game he appears in with this name is WWF Raw.
When he left WWF for WCW in 1996, he took the name Syxx because he was the sixth member of the nWo. He appears with this name in WCW Nitro and WCW vs. nWo: World Tour.
When he returned to WWF in 1998, he was briefly known as The Kid again before deciding to be called X-Pac, which he kept from then on in WWF/E and thusly in every game as well.