I think I would have to say Flipper was my favorite animal hero. I was always amazed at how the two boys could communicate with Flipper. Flipper certainly got a lot done despite not being able to get out of the water.
I am not sure these would be considered heroes. But, I loved Charlie, the Lonesome Cougar. Also, there was a book I read in elementary school called "Champion Dog, Prince Tom". I had a copy of it and wore it out from reading it so many times. It was the true story of Tom, a Cocker Spaniel, who could do all sorts of neat tricks. I can still remember that he could push a baby stroller.