Ratchet

Ratchet (Red Alert) was once a fierce warrior. It was not until he was seriously wounded, losing his hand permanently in battle, that he was able to sit back and realize how terrible war is. He is now a reluctant fighter, and somewhat emotionally detached, preferring to repair his friends than tear his enemies to shreds. This does not mean he is now a coward. To the contrary, when a fellow Cybertron (Autobot) on the battlefield needs his immediate medical attention, he will be there no matter what it takes. He's a brilliant medic and scientist, but he's also extremely cautious.

His nominal micron (Mini-Con) partner is Hook (Longarm), though during the search for the Planet Forces (Cyber Planet Keys), he was accompanied to Speedia (Velocitron) by Drift (Dirt Boss).

(Source: Transformers Wiki, edited)