Bumblebee

Bumblebee is one of Optimus Prime's most trusted lieutenants. Although he is not the strongest or most powerful of the Autobots, Bumblebee more than makes up for this with a bottomless well of luck, determination and bravery. He would gladly give his life to protect others and stop the Decepticons.
Badly damaged in battle, Bumblebee lost the ability to speak verbally, though he can still communicate over inter-Autobot frequencies (in a fashion that seems somewhat akin to instant messaging, a usable but more distant and less personal means of interaction).