Donovan was a mercenary in the same band as Guts and Gambino.
SpoilerHe took an interest in the young Guts and offered Gambino three silver coins to have him for the night, unbeknownst to Guts. When night came, Donovan went into Guts' tent and after a small struggle, forced himself onto the boy while telling him that Gambino was the one who prostituted him. After that night, he is murdered by Guts, who followed him to a secluded spot during a battle.