Morph is a mutant and member of the X-Men.
Morph was a member of the X-Men. He was fun-loving, irreverent, and jovial, described by Wolverine as "The only one who could ever make me laugh." As a result, he and Wolverine were very close, possibly closer than Logan was with anyone else on the team, except for Jean Grey.
Morph was seemingly killed during the team's first encounter with the Sentinels, during the raid on the Mutant Control Agency headquarters. His death hit all of the X-Men hard, and drove a powerful wedge between Wolverine and Cyclops, who was forced to make the call to leave him and Beast behind during the X-Men's retreat.
He later returned as an agent of Mister Sinister, harboring vengeful feelings towards the X-Men for leaving him behind. Posing as a priest, he performed a fake wedding for Cyclops and Jean Grey, luring the couple to an uninhabited island for their honeymoon, where they were ambushed by Sinister and the Nasty Boys. Simultaneously, he sowed discord among the X-Men by sending Jubilee to the headquarters of the Friends of Humanity, inciting Gambit to kiss Rogue (and suffer the ill effects of her power) just before an important mission, and perhaps most importantly, luring Professor Xavier and Magneto to Antarctica, where they were stripped of their powers and forced to fend for themselves in the Savage Land throughout the majority of the series' second season.
It turned out that the vengeful Morph and the Morph the X-Men knew were two separate personalities, the former implanted by Sinister as a way to control him. Eventually, Morph fought his dark side and came to the aid of his former teammates, assisting Cyclops in the climactic battle against Sinister in the Savage Land.
Following these events, Morph was sent to Muir Island for treatment. After some time, he insisted on returning to the team, despite the strenuous objections of Moira MacTaggart. When he returned, however, his first mission involved the Sentinels once more. Morph was paralyzed with fear at having to face the beings that had come so close to killing him.
Eventually, Morph overcame his fear, and even managed to destroy the remains of Master Mold. He once again left the X-Men after this mission, feeling that he wasn't ready to be a hero yet.
He was called into action one last time when Professor Xavier was shot by Henry Peter Gyrich. Impersonating the Professor, he reached out to the mutants of the world, imploring them not to strike back at all of humanity for the actions of one bigot. He was shown with Magneto and the other X-Men in the series' final shot, implying that he remains an X-Man after Xavier's departure.
Morph is a shapeshifter, transforming his body and voice to impersonate anyone he desires, much like Mystique. While he can approximate the powers of people with physical mutations, he does not gain the powers of any other mutant he turns into, nor are his naturally-shifted weapons as strong as synthetic materials (i.e. if he becomes Wolverine, his claws are more fragile than the latter's adamantium).
Morph was voiced by Ron Rubin.
Morph was made specifically for the series, though he is based off a character named Changeling, also known as Kevin Sydney. He was created as a throwaway character, intended to die so the producers could show off the dangers the X-Men face. He became so popular they reintroduced him for the second season.