Originally a fish in the Mississippi River that migrated south in the winter. Term was then applied in the 1830's to lead miners from Missouri. Northern miners without houses who stayed for the winter lived underground and were nicknamed Badgers and Gophers. Southerners who would go south each winter were called suckers like the fish. They would return each spring to buy worthless mining claims. Hence the term was coined. This is also why Missouri is now the show-me-state.
He sold his worthless mined out claim to a sucker.