This page contains information regarding Star Trek: Discovery, and thus may contain spoilers.
"You are no longer alone."
Su'Kal was a male Kelpien. He was the son of Issa, the last survivor of the Kelpien vessel KSF Khi'eth. His name roughly translated from the Kelpien language as "Beloved gift"; in Kelpien culture, the name was traditionally bestowed on the next child born after a disaster (in this case, the ship's crash).
When the Khi'eth crashed on a planet in the Verubin Nebula, Issa – knowing she was dying and that rescue was unlikely – created a vast holographic environment to sustain her son's needs. Due to radiation exposure from the nebula whilst in utero he developed a connection with his surroundings; the planet's large dilithium reserves. When he was approximately four years old, Su'Kal inadvertently caused the Burn when he emitted a powerful psychic shockwave, which triggered the nearby dilithium. (DIS: "Su'Kal") The psychic scream was triggered by Su'Kal's shock and trauma at watching his mother's death. (DIS: "That Hope Is You, Part 2")
Eventually, Su'Kal was found by the crew of the USS Discovery in 3189. He became afraid of Michael Burnham, Hugh Culber, and Saru when they explained they were from "outside", but warmed to them when he believed they were holographic characters from within his simulation. At the appearance of a holographic monster, Saru stayed with him and sang him a lullaby, calming him and preventing another Burn from occurring. (DIS: "Su'Kal")