The Storm God is a deity in the religion of the Drowned God, followed in the Iron Islands of Westeros. He is the enemy of the Drowned God and the ironborn.
The Storm God is believed to dwell in a castle in the clouds and to send winds and waves to lure ironborn off course or wreck their ships. Ironborn believe that it was the Storm God who blew the Andals into the Iron Islands.
In the books
In the A Song of Ice and Fire novels, the Storm God is the "evil" deity in the ironborn religion, fighting against their creator, the Drowned God. The mythos of the ironborn religion is loosely inspired by real-life Viking mythology.