Ratchet (TFA)

Before the Great Wars, Ratchet was a civilian mechanic, and one of the best on all of Cybertron. But war is hell, and Ratchet learned that all too well. It left him bitter and cynical. After the war, he got himself placed in a dead end position of repairing space bridges, seeing it as a chance to get away from what he had experienced. And in his experience, "hero" is another word for casualty, because that's what most of the heroes ended up being. Still, he knows one when he sees it, and Optimus Prime definitely is one. He enjoys grumbling about almost everything, being sarcastic, and having war flashbacks, just like any old man.