In 1916, Tolkien started imagining the worlds which would be the settings for his classic fantasy tales.
He set out the myths and legends of the First Age of Middle Earth in The Book of Lost Tales.
But it wasn't published until after he died. It came out eventually in 1997 and was called The Silmarillion.
He also started sketching out other ideas and characters. One of them was Bilbo Baggins, the hobbit.
What eventually became The Hobbit was meant to be bedtime stories for his children about the adventures of a little gnome-like fella with hairy feet!
But it was published in 1937.