Gideon was a really cool concept for an X-Men villain that always had a lot of potential. Unfortunately, he had a really short life span before he was killed by the mutant vampire Selene. that said, he’s still cool in my book.
He was born in the fifteenth century and served as a crew member for Christopher Columbus’ New World voyage. After being left for dead, Gideon discovered that he was nearly immortal. Not only is he a mutant with the power to mimic the skills and abilities of the people around him, but he also belongs to the subspecies of Externals which have the gift of immortality. Gideon isn’t the type of villain in the Doctor Doom style, that wants world domination, nor is he like the Joker and wants to be an agent of chaos. Instead, Gideon spent his time lurking in the background manipulating the people around him for his own gain and amassed a fortune.
Gideon made himself publicly known around the same time as the original X-Force debuted, as he was interested in mentoring Sunspot whom was believed to be another External. In order to get closer to the younger mutant, Gideon had his father brutally murdered. It turned out that Sunspot wasn’t an External, and it was really Cannonball instead. Eventually the truth was revealed and this put him at odds with X-Force for the rest of his life. Although he never became a full on villain, he did have an odd respect of Sunspot, Cannonball and the rest of X-Force. Towards the end of his life when he feared Selene was going to murder him he reached out to him for assistance. Unfortunately, they got the message too late.
Gideon was an interesting character and the possibilities of what the could do were endless. It’s a shame he hasn’t been brought back to the land of the living.
Ridiculously Awesome 
Gideon was kinda meh. He was very much a product of his time. He was far from the worst character Liefeld created, but he did have a few typical Liefeld design cliches. The X-Ternals as a group just weren’t terribly compelling.