Gerav is tasked to capture the Hawke.
Background
Gerav is a member of the Carta and also an acquaintance of Varric. Gerav also constructed Bianca for Varric.
Involvement
Hawke encounters Gerav in the Carta fortress, like the rest of the Dwarves there, Gerav is insane and has been corrupted by the Darkspawn taint. If Varric is in the party, he will attempt to talk to Gerav, but decides to put him out of his misery. Gerav manages to avoid the shot and summons allies, much to Varric's dismay and anger. Once defeated, Varric revealed that Gerav wanted to design a repeating crossbow, and that Bianca was the only one that worked.
Gerav fights like any other Carta assassin, he will attempt to flank the player and backstab them, he will also be joined by other Carta members, including a couple of assassins.
If Varric is not present, then Gerav will still appear but he will attack Hawke on sight. He will still be joined by Carta allies and still drops the same loot.
Result
If Varric is in the party, he will tell Hawke that Gerav made Bianca. Once Gerav is out of the way, Hawke can continue further into the Carta base. Gerav will drop a ring that only Varric can wear. If Varric is not in the party, then another party memeber will comment on Gerav's insanity, but his involvment with Varric's past is not revealed.
Drops
Quotes
"The Hawke's blood! The Master will rise. He will be free!"
"The Master must be free..."
"We drink the darkspawn blood. He calls us..."
"It's the only way...to hear the music."
"The Master is calling. He needs the blood."