Trinimac was an ancient Aedroth (Et'Ada or "Original Spirit"), Aldmeri deity, and the alleged precursor to the Daedric Prince Malacath. He is described as the strongest of the Aedra, the champion of the High Elven pantheon, and in some places more popular than Auri-El. Trinimac is referred to as the champion of Auri-El himself.
The official view taken by the majority of the leading priests in Orsinium, put forth by king Gortwog gro-Nagorm, is that Trinimac still lives and Malacath is a separate entity, an impostor. A handful of Orcs within Orsinium and the majority of the Orsimer diaspora view Gortwog's beliefs as heresy. Malacath is referred to as the reanimated dung of Trinimac.
During the climax of the great war between Auri-El and Lorkhan, Trinimac who was Auriel's greatest knight, knocked down Lorkhan in front of his army and tore out his heart, intending to destroy it. As the Trickster God was finished, the Men dragged Lorkhan's body away from the battlefield and swore blood vengeance on the heirs of Auriel for all time.
However, when Trinimac and Auriel tried to destroy the Heart of Lorkhan, it laughed at them. It said, 'This Heart is the heart of the world, for one was made to satisfy the other.' So Auriel fastened the thing to an arrow and let it fly long into the sea, where no aspect of the new world may ever find it.
During the exodus of the Chimer in the Mythic Era, Trinimac who was one of the most powerful Aldmeri deities at the time, tried to stop the movement. The Daedric Prince Boethiah, mastermind of the movement, confronted Trinimac, and transformed him into the Daedric Prince Malacath. As a result, Trinimac's followers were changed as well into what are now known as the Orsimer (Orcs), some of which worship Malacath as their god.