Mikrul was the youngest son of Arch-Mage Gauldur. Along with his two brothers, Jyrik and Sigdis, he coveted the power of his father's amulet. After recovering the artifact, it was split into three pieces.
In their lust for power, the brothers each took one for their own, and used them to summon armies to destroy the cities of Skyrim. Arch-Mage Geirmund of Windhelm led a battalion of battlemages to end the murder spree, and seal the brothers in their respective tombs with Writs of Sealing. 
Writ of Sealing Edit
"Be bound here Mikrul, Murderer, Betrayer.
Condemned for your crimes against the realm and the lord.
May your name and your deeds be forgotten forever.
And the charm which you bear, be sealed by our ward."
When encountered, he summons Draugr Thralls to distract the Dragonborn during battle. When killed, his corpse contains the Gauldur Blackblade which is an enchanted Ancient Nord Sword that absorbs 5-25 points of health depending on player level, as well as other random loot. He also has a writ of sealing on him, which says that he is a murderer and betrayer.
After recovering all three amulet fragments, the Dragonborn must head to Reachwater Rock to reforge the Gauldur Amulet. There, the three Gauldurson brothers are fought a final time. Mikrul is the first to be fought and he summons between one and three thralls to battle alongside him. He prefers to do melee battle.
- Mikrul's surname is a common Scandinavian patronymic (Gauldurson = Gauldur's son).
- The Blackblade may appear on a thrall, rather than on Mikrul himself.
- Sometimes he is already off his sarcophagus when the player arrives, his body may become unlootable at such occasion. To fix this bug, exit and reenter the location.