When the Isthmus Keep is a beset by monsters, Lord Rudolf orders his children to flee and warn Prince Neidhart in Crystal City, the capital of Rosalia. Lord Rudolf decides to stay behind with his wife to fight off the rampaging horde of monsters. After a fierce battle, with the defenders defeating 10 times their own numbers, Lord Rudolf finally falls in battle and the Keep is lost.
Visiting Isthmus Keep after it's destruction, you can make your way upstairs into Lord Rudolf's room. Walk around his desk and examine the diary to hear extracts from Rudolf's life.