The Broker was a bounty hunter hired to capture Lillith Daturai by Lillith's sisters: Nephitiri, Nethspira, and Bellenore. When Vox Machina encountered him, the Broker was accompanied by an old witch and a muscular warrior wearing a white, featureless mask. As an NPC, he was played by Matthew Mercer.
The Broker was a male red tiefling with slicked-back, black hair.
The Broker was hired by Lillith's sisters to capture her.
"Crimson Diplomacy" (1x25)
Lillith's cousin, Zahra Hydris, had spoken highly of Vox Machina to her in the past, so Lillith sought them out for aid. She disguised herself as a serving girl in Sovereign Uriel's palace, revealing herself during a fight against the Briarwoods.
After aiding Vox Machina in the fight with the Briarwoods, a red eye-mark began to glow across Lillith's chest. It revealed that the Broker knew where she was and that he'd been using scrying to track her down.
On the way back to Greyskull Keep, the Broker approached Vox Machina and explained that his quarrel wasn't with them—that he only wanted Lillith. Emotionally charged and impatient from the night's previous ordeal, Vox Machina quickly reacted in defense of both themselves and Lillith.
The old woman was put to sleep during most of the fight, and when she tried to run away, Tiberius killed her with a telekinetically-controlled, spinning, five-pointed throwing weapon. (This was a controversial kill, both within the group and among the other notable citizens of Emon, which contributed to Vox Machina being kicked off the Council of Tal'Dorei.)
The Broker himself was easily beaten due to most of his movements and spells being stopped by Tiberius. Percy—frustrated with the Briarwoods' escape—killed the Broker by repeatedly shooting him through the chest, yelling out, "Your soul is now forfeit!" Lillith reanimated the Broker's corpse and sent him back to her sisters with a message to leave her alone.
The Broker's masked warrior companion was restrained, and he explained that he fought for the Broker because the Broker gave him purpose. Lillith suggested that he join the Slayer's Take in Vasselheim to find new purpose, then set him free.