Eulerex is a very cold fallen who cares nothing for others, wishing only to fight the races. He is a strategic thinker who's always composed, examining any situation calmly.

He is willing to kill anyone who gets in his way or disrupt your plans, including fallen and Demon kings, as he did not hesitate to attack Krebskulm and Edelgard, when he learned that he did not want war.

He is willing to sacrifice fallen, how many required, if that is what it takes to achieve the objective. He is quite selfish, as his desire to annihilate the races is above all for him.

when someone is threatening his position in charge of the Demon King Army, he will quickly plot his destruction, as he let members of the Vahl faction be sacrificed for Modinalam's 《Ruination Flame》, or when he sent Ryoka alone against the hero of Faltra City, with the intention that she dies and arouses the blood thirst of Modinalam.

While the fallen see the Demon King as a being to be worshiped, he sees them as another weapon for the destruction of races.