Rhax

Rhax's life until recent was nothing of note.
He was a warrior, as many Lizardfolk are, within his tribe.  
He  was no stranger to losing friends and allies in battle, desensitised   to death in most all manner of ways; even being taught that eating your  fallen allies is a better use of resources than to bury them.

A  particularly savage attack left the  tribe in shambles with few  survivors - Rhax included. They saw little point in trying to rebuild,  so set off in separate ways to find their own ways to survive. He set  off towards the bigger cities in hope of finding a band of adventurers;  it's easier to stay fed when you aren't hunting alone.

Upon meeting the party he realised two things:
If they know what they're doing, he'll get fed.
If they don't know what they're doing... he'll feed himself.
So, he agrees to join - willing to get his hands dirty so long as  there's a meal at the end of it.
...And maybe relearn how to care for your comrades along the way.
Now he's peas in a pod with the party, with a particular soft spot for Trivet the aarakocra.