Bucky the Rat

Copy/pasting some bio info this time...

The creator of the experiments, Buck Stein was originally a human until an accident transformed him into an electricity-controlling rat. Shunned, even hunted by human society, Bucky found comfort and love with a Raven named Hope.
Together with Hope, he worked on experiments to create life. After Hope's murder at the hands of GUN, Bucky turned his experiments towards the goal of vengeance. But when his plans went awry and came to threaten the world, Bucky snapped out of it and helped to set things right. He has since been mostly benign in his experimentations...

He was transformed into a rat roughly 50 years prior to the "present", but the transformation stopped his aging process, so he still looks pretty young.