They never explored it in this series, but in the comics Lucifer is the person to paralyze him, 由 dropping a large stone on his spine, long before the X-men ever formed. Then he gains use of his legs after the Shi'ar empire uses their technology to heal them and they are later shattered again 由 the Shadow King. Then the mutant Xorn heals him using his powers so he can once again walk. Then Magneto re-paralyzes Xavier. So he's been paralyzed 由 quite a few people, but Lucifer was the first to do so.
In the series it was blamed on Xavier's brother aka Jugernaut. Though I've heard so many versions of it and I can't get a hold of the comics to explore. But yeah Jugernaut was the supposed reason in X-Men: Evolution In the other tv series it was blamed on WWII Then we've got x-menobsessed's explanation
