Elvis Urkel (played by Jaleel White) is an alter-ego of Steve Urkel. season 6 episode 17 Ain't Nothing but an Urkel.
Steve tries to impress an MIT college recruiter, but due to being nervous about the interview, he again calls Laura Winslow for assistance to his lab in the basement. After showing her the formulas he has for his experiment he wants to use for the interview, he accidentally trips and gets the two mixed up and is confused to which could be which, as he assumed the one he picked would be right, he uses that to fix up the juice for his transformation chamber. After the transforming process, he steps out as a Albert Einstein variant however the moment is short lived when the transformation backfires as his mustache disappears and his hair turns from white to black and his accent changes until he started looking more like Elvis.
After the Accidental transformation to Elvis was able to still obtain his Urkel personality for a little bit which kept switching to Elvis's personality back and forth as he tried to find a way to switch back to Einstein however while trying to go shopping for a cure the Elvis personality took over fully and instead of coming back with a few things to turn to Einstein, he returned with Elvis's costume and sunglasses instead.