The mirror universe counterpart of Sarek, a bearded Vulcan called the Prophet who serves the anti-Terran rebellion and uses a mind meld to judge whether Michael Burnham can be trusted.
The mirror Sarek appears in The Wolf Inside, played by James Frain. He lives among the coalition of Klingons, Vulcans, Andorians and Tellarites hiding on Harlak under the leadership of the Fire Wolf.
When Burnham, posing as her Terran double, beams down to warn the rebels instead of destroying them, the Fire Wolf asks the Prophet to look into her mind. In the meld he sees her memories of another Sarek who raised her and of a universe built on cooperation, and declares that she means them no harm.
His verdict buys the rebels time to evacuate. Soon afterwards the Emperor's ship bombards Harlak from orbit, and the series leaves his fate unstated.