Lorkhan is a deity found in every Tamrielic mythic tradition and portrayed as a creator, trickster, and tester. He convinced, contrived, and tricked the et'Ada (original spirits) into giving up themselves or parts of themselves to create Mundus (the universe, planet Nirn where TES takes place) which upset the status quo.
Magnus, the architect of Mundus saw the trap and pulled away at the last second and fled to Aetherius, tearing a hole in the sky that became the sun. Akatosh saw the trap as well but did not flee and instead threw himself into Mundus. He landed in what became known as the Isle of Balfiera in High Rock and his full presence caused all spirits and chaotic forms of creation to crystallize and time to become linear and ordered. Adamantine Tower, later called Direnni Tower and the oldest known structure in Tamriel once used by Lorkhan to discuss the creation of Mundus was later used by the gods to discuss Lorkhan’s punishment.
Lorkhan’s heart was torn from his chest by Trinimac and fastened to an arrow by Auri-El who fired it into the sea of the mortal plane. It hit the earth as a fiery meteor to form the Red Mountain and Vvardenfell, the Star-Wounded East. Lorkhan, mutilated and separated from his divine center continued to be revered and remembered in the memories and minds of mortals. It is said Nirn never had rain until Lorkhan was forcibly separated from his divine center.
He is considered the most unholy of all higher powers by the High Elves and a hero to all mankind. Nirn's moons, Masser and Secunda are his "Flesh-Divinity", literally his corpse and represent the "Cloven Duality", or dichotomy of opposites that is central to Mundus and Lorkhan's ideas. Masser and Secunda are considered ‘guardians of mortals’ and are themselves mortal. Masser the largest has long since died and its red color is caused by its decay.
The Heart of Lorkhan could be found in the Heart Chamber of the Dwarven Citadel in Morrowind where it was visited annually by the Tribunal to renew their powers. When Dagoth Ur was awakened he tried to harness its powers to construct a walking god called Akulakhan but the Nerevarine destroyed the heart. Although it no longer has a physical form and was a large part of Lorkhan’s spirit it still holds influence over the world, Nirn.
Lorkhan is said to still have a presence and take the form of diverse avatars, incarnations and historical patterns. Mankar Camoran claimed that Lorkhan is a daedra whose daedric plane is "Dawn's Beauty ... misnamed Tamriel by deluded mortals".
"But 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." -The Monomyth
"Beneath Red Mountain, Dwemer miners discovered a great magical stone. By diverse methods, Lord Kagrenac, High Priest and Magecrafter of the ancient Dwemer, determined that this magical stone was the heart of the god Lorkhan, cast here in the Dawn Era as a punishment for his mischief in creating the mortal world. " -Kagrenac's Tools