TransFormers Animated Wreck-Gar

While the robot characters in TransFormers Animated weren't particularly plentiful, what they lacked in numbers, they more than made up for in personality. The small cast seemed to have been perfectly selected for what they were able to add to the storytelling potential of their situation.

A prime example of this would be Wreck-Gar, who was given an entirely new origin story - no longer leader of the Junkions, a race of transforming (and partsforming) robots which evolved separately from those of Cybertron - he was, instead, the innocent creation of Sari Sumdac's AllSpark key. Introduced with no idea of his own identity, his occasional appearances served to develop his character, though I seem to recall his fate was left very open-ended.

Reveal the Shield Wreck-Gar

The 1986 Animated movie came under a lot of fire for a lot of reasons (killing Optimus Prime, replacing him with the slightly rubbish Rodimus Prime, etc., etc.), but it's rarely acknowledged for the fun, new characters it brought to the table... largely because the toys were so poor. Wreck-Gar, leader of the Junkions (sentient transforming robots who seem to have had some kind of parallel evolution to Cybertronians, and were built out of junk) was a prime example. Cursed with a crummy toy that looked nothing like the animation model, he was, nevertheless, an amusing character, not least thanks to Eric Idle's voice work. Ignored until TransFormers Animated, Wreck-Gar - along with some other Junkions - has enjoyed something of a renaissance since, and the Reveal the Shield branch of Classics/Universe took him back to his roots.