You had me up until the blunt-force amnesia thing and "Being stronger then most Tigris..." Ugh. Have you ever been hit on the head? You want to stay still for a little bit, right? Now imagine that that blunt-force trauma is first of all heavy enough to rattle your hippocampus, and enough to cause long-term retrograde amnesia (for reference, people in car crashes are usually unable to recall the last few seconds of the actual crash, but can remember things before and after.) He wouldn't be getting up, and due to that, he first of all definitely wouldn't be "stronger than most Tigris" and would've probably been killed due to being incapacitated. Though, if he's the *last* Tigris, I suppose he'd be stronger regardless, eh?
Likewise, an outsider becoming the leader of "one of the most power bands of thieves" in "mere months"? I'm not saying it's not possible, but that sounds awfully implausible.
In short: that sounds like an incredibly cliche, amateurish deux ex machina to create the main storyline.