David is one of the first companions you get in The Technomancer. He specializes in Guardian style, so he can benefit from an extra shield or mace you have lying around.
David's a little brash. He's not really a fan of technomancers, and he lets you know it....all day long.
The saving grace is that he does learn to tolerate you over time.
As a Guardian, David's role is basically to just distract enemies from you and the third companion. He honestly doesn't seem to do much damage, even if you set him to Offense mode. Instead, you're probably better off just keeping him on Defense and letting him distract a few enemies, then you can come back and kill them later.
David provides a +2% to Resistance of Disruption. He doesn't have an Ally bonus though. Partially because...
Spoiler alert - David doesn't stay with you very long. I won't get into details, but let's just say you shouldn't get too attached to this feisty soldier!