William the Lion, sometimes styled William I, also known by the nickname Garbh, "the Rough",(c 1143 – 4 December 1214) reigns as King of the Scots from 1165 to 1214.

His reign is the second longest in Scottish history before the Act of Union with England in 1707, (James VI's is the longest, 1567–1625).

He become sKing following his brother Malcolm IV's death on 9 December 1165 and is crowned on 24 December 1165.