Ormund was Hand of the King to Aegon V Targaryen and commanded the royal forces against Maelys Blackfyre during the War of the Ninepenny Kings. He died in the fighting at the Stepstones, and according to singers, he spent his dying moments in the arms of his son, Steffon.
In the books
According to The World of Ice and Fire, Ormund was the heir of Lyonel Baratheon, who rebelled against King Aegon V, until Ormund himself was betrothed to the King's daughter, Rhaelle Targaryen. He later became Hand of the King to Jaehaerys II, his brother-in-law. This is different from the continuity of the show, in which Jaehaerys has been removed.
While fighting at the Stepstones at the head of the royal forces, Ormund was killed by Maelys and died in the arms of Steffon. Command of the royal forces passed to Ser Gerold Hightower, Lord Commander of the Kingsguard.