The Mysterious Character Has The Ability To Turn Into A Super Saiyanjin.
It's probably Future Gohan. He has the same jacket as Future Trunks.
He has a scouter that particularly Saiyans use. I guess he got that right after Raditz died. Raditz had green scouter, as well as that Gohan has.
He has the style of Earthlings. People from outer space with scouters use armors.
Appearance matches somewhat.