Sirius

 is the warlock patron of Zahra Hydris. Sirius has not appeared on the show.

Background
Very little is known about Sirius but he supposedly had entrusted Zhara Hydris with watching over and judging Vox Machina. The mysterious patron helped in the resurrection of Velora Vesar after the Battle of Vasselheim after Zarha gave her judgement on Vox Machina.