who was the first baseball player to hit a homerun?

“The first home run ever hit in the National League was by Ross Barnes of the Chicago White Stockings (now known as the Chicago Cubs), in 1876.”
-from Wikipedia

Ross Barnes is a good answer…but I’d argue that it’s impossible to answer, considering that the true origins of the sport are still shrouded in mystery and there was a lot of baseball played before the formation of the National League.

The Abner Doubleday story is endearing…but ultimately untrue. I’d highly suggest Ken Burns’ Baseball. If you’re interested in the history of the game it’s a great primer or refresher.