When you first meet Andrew, he goes by the name Lucky and introduces himself as a traveling merchant. He asks you to set up a meeting with him and Master Connor, which is an interesting little side quest.
Later he becomes your companion, and is one of my personal favorites. Andrew is also the only male romance option in The Technomancer.
Andrew's personality turned me off at first, but grew on me once I learned more about him. Without giving any spoilers, let's just say he's had a rough life. But as you get to know him, you realize that he's a good, reasonable guy.
The missing left arm is probably all the evidence you need of that.
It's tough to discuss combat without giving too much away, so I'll just say its another spoiler -- when you first get Andrew, all he can use is a mace. After all, you're limited when you only have one arm.
But when you complete his quest, he gains access to technomancer abilities. Booyah!
Having Andrew in your party gives you 5% extra Fluid Regeneration. Once you get his Ally bonus, you get +1 Charisma.
Your first quest with Andrew involves setting up a meeting with him and Master Connor. Don't make the same mistake I did -- actually follow Master Connor once you go get him! I was messing around in my inventory and the quest completed without me getting credit.
Anyways, later you have to help Andrew get himself set up with his technomancy stuff. It's probably the best companion quest in the game, as it is the only one that changes how a companion fights.