Howard the Duck was born on Duckworld, a planet in another dimension, where intelligent life evolved from waterfowl. Duckworld is apparently an alternate Earth, and resembles mankind's Earth in an astounding number of ways, including the fact that ducks speak English. Very little is known about Howard's past on Duckworld. Indeed, there are conflicting accounts as to the circumstances surrounding his disappearance.
More on this character soon, for the meantime read his bio here: