Zs'Skayr was the high Ecto-Lord of the planet Anur Phaetos. he learned about the omnitrix when one of Vilgax's data-probes crash-landed. He read its files and met up with Myaax(One of Vilgax's species) and assisted her in aqquiring DNA samples for the omnitrix in the nearby planet of Flors Verdance. Unknown to Myaax, Zs'Skayr possesed the Florauna and used it and his powers to allow his DNA to enter the omnitrix. In the process, as an Ectonurite's conciousness exits even in a strand of DNA, a copy of him was trapped inside the omnitrix in a real Ectonurite's form, not Zs'Skayr's Ecto-Lord form thus creating a clone(This was not mentioned in the series but when the Ben 10 Marathon Week talked about his origin, it was obvious that he created a clone). The real Zs"Skayr is not heard of anymore but his clone is the one which is Ben's enemy.
Zs'Skayr first appeared in the episode "Ghostfreaked Out". In this episode, he forces his way out of the omnitrix and decides to posses Ben to control the omnitrix. He recruits Thumbskull, Acid-Breath and Frightwing to get Ben but Grandpa and Gwen beat the Freaks while Ben kills Zs'Skayr by exposing him to sunlight. Zs'Skayr is the main antagonist of the third season in the four connecting episodes: "Benwolf", "Under Wraps", "The Return" and "Be Afraid of the Dark" which he appears in only "The Return" and "Be Afraid of the Dark". In the two episodes, he is ressurected by an alien scientist named Dr Vicktor and decides to plunge the Earth into total darkness but Grandpa Max destroys the transmitter which transmitted the corrodium beam to block out the Earth while Gwen kills Zs'Skayr by exposing him to sunlight again. Ben gains Zs'Skayr's form in the omnitrix again but as his Ecto-Lord form and ben never uses the form. Zs'Skayr returns in Ben 10 Alien Force. Apparently, when the omnitrix scanned him while he tried to grab it and put his DNA back in the Codon Stream. But he was removed and imprisoned by the Galvans. Vilgax frees him on the term that he tells him the secrets of the omnitrix. Zs'Skayr tells him and Vilgax frees him but Zs'Skayr betrays him and starts to posess the people of Vilgaxia, Vilgax's home planet. Vilgax enlists the help of Ben, Gwen and Kevin to defeat Zs'Skayr and free his people. in the ensuing battle, Ben allows Zs'Skayr to enter his body so the omnitrix will aqquire his DNA so Ben will transform into Ghostfreak and posess Zs'Skayr but Zs'Skayr posses him. Vilgax kills Zs'Skayr by exposing him to the light from his sword and frees Ben and his people.