Mathlann

Mathlann, the Lord of the Deeps is the High Elf Poseidon, except he doesn't rape virgin brides on their wedding night, making for the rare case of Warhammer being less Grimdark than something it cribbed from real life, though it's probably partially because Warhammer in either incarnation is one of the most sexless and romanceless settings ever intended for teenagers and adults.

Warhammer Fantasy

Mathlann likes creating sea monsters for kicks and creating storms by practicing his belly flop in the middle of the ocean. He's also a god of horses to a small extent, although it's likely because he's Kurnous's buddy rather than him creating horses in the first place. Most elves think of him as evil and a god you only try to not piss off like Khaine, but Cothique holds him as their patron god above Asuryan due to their manly belief that wrestling sea monsters bare-chested is something that should be done whenever possible, and the elves of Lothern think he's a bro since their sea monsters tend to ignore elves and their allies while consuming Dark Elf and Norsemen ships whole. While this is technically HERESY, elves from other regions just bitch and make fun of them instead of FWIPing them. So far he's saved Sea Lord Aislinn, the admiral of the Lothern fleets in peacetime and the entire High Elf fleet from all kingdoms in times of war, three times from being killed making Aislinn the closest thing Mathlann has ever had to a mortal champion. In addition, the sailors of Cothique vessels are as devoted to him as any priest. There is also a human god, Manann, who is identical to him, and may in fact just be Mathlann under a different name.

Age of Sigmar

He’s still dead, though he has followers in the form of the Idoneth Deepkin. When enough of their astral dead are summoned they create the ‘Eidolon of Mathlann’ a big guy whose cape is practially the shitting ocean, and the model looks overall amazing! In a strange irony, he's getting possibly more attention by Games Workshop via his own army of followers posthumously than he ever got in life.