Bugs Bunny's hunched-over walk and eyebrow-wagging are imitations of Groucho Marx. The evil scientist is a caricature of Peter Lorre.
The orange monster has no name in this cartoon. He is known as Rudolph in Water, Water Every Hare, then as Gossamer in Duck Dodgers and the Return of the 24½th Century. The latter name is the one most familiar to cartoon fans.