He is an assassin who has worked for multiple people, including Greil, Ike, Bastian, and Izuka. He demands gold for whatever job he takes on, regardless of how large or small, though his reasons for amassing so much gold are unknown. (Elincia goes so far as to ask him about this in an optional conversation in Radiant Dawn, but he demands an exorbitant amount of gold for an answer.) He even demands Ike to pay him when asked to show up to dinner with the group. He can apparently be reached by going to a bar and asking for a "fireman". As an assassin, Volke is willing to take any job, no matter how "dirty" it is, and once he takes a mission, he devotes himself to completing it, regardless of how long it would take. He only takes one job at a time, as shown in his support conversation with Bastian and attack conversation with Izuka in Radiant Dawn.
Path of Radiance
Volke is an assassin throughout the events of the game, but this is not revealed until late into the storyline, after he is paid the 50,000 gold that he demands of Ike upon their initial encounter. When this has happened, he reveals the truth about Ike's parents, Lehran's Medallion, and the fact that he is an assassin hired by Greil to kill Greil if ever he was to go berserk again. Afterwards, Ike pays him from the 50,000 to renew Greil's contract with Ike. (But in the sequel, Radiant Dawn, he pays Ike back 20,000 of his 50,000 gold upon encountering him.) Upon hiring Volke (upon the second time the two options: Hire or Don't Hire) for renewing Greil's contract to Ike, if the player chooses "Hire", Volke automatically Class changes into an assassin.
Volke appears late in the events of the game, hired by Bastian to capture Izuka. You can recruit him with Bastian or Elincia, by paying him a certain amount of gold. Most of it can be reclaimed in his Info Conversation on the next chapter. As in the end of Path of Radiance, he is an assassin. In his battle conversation with Izuka, it is revealed Volke once worked for him. He also shows some slight modesty and humility when he flusters after Ike thanks him for his services. He is, unlike in the previous game, not an important part of the overall plot.