Before Conan became king of Aquilonia, Trocero tried to invade Aquilonia himself, but failed to seize it. However, this has made it problematic for him to command the forces of Aquilonia when the country is under invasion and Conan is absent, because the people of Aquilonia remember how Trocero himself once tried to invade Aquilonia.
During the Nemedian invasion, Trocero and his knights were driven from Tarantia when Conan was thought to be dead. This left Tarantia unprotected and the Nemedians were able to seize the city, effectively getting power over most of Aquilonia. Trocero and his knights were however joined by Conan, and together they seized back Aquilonia from the Nemedians.
When King Amalrus of Ophir led Conan into a trap, capturing Conan the with help of King Strabonus of Koth and the Kothian wizard, Tsotha-lanti. Trocero was left with the duty of defending Aquilonia from the invading forces of Ophir and Koth. Again, however, he was forced to flee from the city of Shamar before the enemy forces reached the city due to the public thinking Trocero himself was going to seize the crown of Aquilonia. Also this time, Trocero played an important role in the recapture of the city after Conan's return.