In Blood Omen, Ottmar was the wise and respected king of Willendorf. He was adored by his people, and he commanded the powerful 'Army of the Last Hope'. Approaching Willendorf, Kain said that "the Lion Throne had once held [his] allegiance"; presumably this meant Kain had once regarded Ottmar as his king. Considering that Kain was born in Coorhagen (a city that appeared to be loyal to Willendorf), and he died wearing white armour - similar to that worn by the Hope soldiers - this seems likely.
Ottmar had a daughter. She was his only child (as far as we know; no others have ever been mentioned). To celebrate the princess' birthday, he announced a dollmaking contest. He promised to grant a royal favour to the winner; the person who "created the finest doll in the realm". Elzevir the Dollmaker won easily, but instead of accepting the royal favour, he just asked for a lock of the princess' hair as repayment. Shortly after, the girl became utterly lifeless. Elzevir had used her hair as part of a spell, and he had stolen her soul.
Kain visited Willendorf at Ariel's suggestion, having already heard of Ottmar's plight from the Oracle of Nosgoth (Moebius). As the Nemesis had grown in power, Ottmar's white-clad army had become the only force left that could possibly halt his conquest of Nosgoth, hence their name: the Army of the Last Hope. They were the last hope the land had of escaping the Nemesis' violent and tyrannical rule. Unfortunately Willendorf was in no state to fight. Kain found Ottmar in mourning for his daughter; a broken man. The "proud militia" of the Hope army were scattered, searching for Elzevir. Ottmar was so desperate that he offered his kingdom to whoever could save his child. Kain noted that the people of Willendorf "worshipped him, even in his weakness".
Kain chose to take up the offer. He hunted and killed Elzevir, and gained the gratitude of the king. He did not take the kingdom; instead he got Ottmar to lead his army into battle against the Legions of the Nemesis. However, the Army of the Last Hope were overwhelmed, and in this conflict - the Battle of the Last Stand - Ottmar was killed.
Following Ottmar's death, the surviving soldiers of the Hope army "fled to the safety of the forest". Kain used a Time Streaming device to escape from the battle. Finding himself fifty years in the past, he killed the boy king, William the Just, preventing William ever becoming the Nemesis, and altering the path of Nosgoth's history. This alteration would also have impacted Ottmar's fate, as the Battle of the Last Stand could not happen without the Nemesis there to instigate it. We do not know what became of Ottmar following Kain's murder of William. However, rest assured that Ottmar, Elzevir and the princess were 'not lost in the time shuffle, they just don't have much to do with Raziel's and Kain's journeys'.¹ That is why their individual stories have not been revisited.