Because he was a slave, the Kelpien did not actually have a name. However, in the mid-2250s Michael Burnham of the prime universe decided she was going to call him Saru, in honor of a respected friend.
While Burnham communicated with the primary universe Saru, he asked if there were any Kelpiens on board the Shenzhou. Burnham decided not to tell Saru about the existence of his mirror counterpart.
In an alternate timeline created by Philippa Georgiou via the Guardian of Forever, Michael Burnham threatened to send the Kelpien to the butcher after he tried to help a fellow Kelpien servant who was going through vahar'ai. However Georgiou intervened, taking him from Burnham's possession. While helping Georgiou get ready for a public appearance, Saru told her what he knew about about Burnham's planned coup. Georgiou then said he would be her eyes and ears for anything happening on the ship. (DIS: "Terra Firma, Part 1") He remained as Georgiou's servant for the next three months she was on Discovery. While brushing Georgiou's hair Saru told her that his vahar'ai had started and he wished to be culled. Georgiou refused, instead telling him that vahar'ai isn't the end of life, instructing him to lock himself away in a room until vahar'ai passed. She also told him of another Kelpien named Saru, who live through vahar'ai and became the captain of a starship. He was shocked by the revaluation that everything he had been taught was a lie and that his entire family had been killed for a lie and he remarked that Georgiou wasn't Terran. Saru was later present when Burnham put her coup into action; he rushed into brig along side Sylvia Tilly, Joann Owosekun, and another Kelpien shooting down Burnham's rebels, Saru himself killed Hugh Culber throwing him into the ceiling. Saru held a dying Georgiou in his arms after her fatal duel with Burnham, before she died, Georgiou noted that Saru had passed through vahar'ai.