You can earn his Achievement easily by completing the tasks to unlock the four characters below.

Tim Bear
Play multiplayer once.

Gaben
Score 2,000 points or chop 999,999 wood total in Single-Player mode.

Bruce Tree
Win 5 rounds in a row. This can be done easily with the help of a friend.

Lucha Timbre
Defeat 5 opponents in a row. This can be done easily with the help of a friend.