Galderian Harnius was a Great Knight lieutenant who, like Nircurus, served as a Great Knight cavalry officer and was given the nickname "Hammering Harnius" due to his advocacy of rapid cavalry assaults and hammer and anvil tactics. Since the cavalry ranks of the Great Knights were different to when commanding solely infantry, Galderian went from being a cavalry captain to Nircurus' lieutenant, although he didn't mind as he usually argued with his superiors about their strategies and was constantly shifting positions anyway, while Nircurus had very similar tactical thinking and was a good friend. Although highly capable in commanding cavalry squadrons, Galderian had a tendency to bicker with those he considered tactically inferior on his own side, and by extension, anything he regarded as ridiculous or illogical, a complaint he often brought up. He was also friends with Parean, Vince, Samson and Yaleris, but he had a certain disdain for their preference to fight on foot (especially Yaleris, who dismounted her squadrons for battle), personally preferring riding on a horse and even going as far to dislike walking.
Regardless, Galderian also served on the Eclipse Expedition, in which he fought alongside Nircurus until the introduction of Kirev as the general of the expedition, rather than Pepin. Kirev's suicidal tactics immediately earned him Galderian's hatred, and during their first assault on a Chaos base in the outskirts of the city of Roval, Galderian outright refused to cooperate with Kirev's orders and openly argued with his general, resulting in him being knocked out and placed under arrest for insubordination.
The next day, Galderian awoke from unconsciousness in a cell, chained up next to Grifo, a low-ranking Great Knight notorious for being a "weasel" and consistently attempting to escape or defy authority through any means possible. In spite of this, the two managed to have a decent conversation reminiscing about their mistakes which wound them up placed under arrest by the Great Knights, until it was revealed that Grifo had in fact sabotaged a mutiny by informing the Juggernauts.
- Galderian is based off two German Nazi generals, namely Heinz Guderian and Erwin Rommel, both of whom were excellent tacticians specialising in Blitzkrieg tactics (and are recognised as not being implicit in the Holocaust), but also had argumentative and caustic personalities, which are reflected in Galderian's character.
- The nickname "Hammering Harnius" is a direct reference to Guderian's nickname as "Hammering Heinz".