In the "Tale of Two Brothers" short story it's a water buffalo that gives Taka his scar. Sorry. I don't buy that. If a water buffalo gashed his face, he'd have much more than just one little scar to show for it. In fact the outcome, I think, is most likely too graphic to even draw out (at least for me o_O)

It's a popular fan theory that his father Ahadi gave him his scar, but I have also seen theories that it was Mufasa...and I sorta like that theory the best. I think it's more than likely that Taka brought it on himself somehow, but Mufasa always seemed to have somewhat of a short fuse; it might've been worse as an adolescent. "Temper, temper!" XD