Ensign Beckett Mariner served in the command division of the U.S.S. Cerritos in 2380. She had previously served with five other ships, including the U.S.S. Quito while it made first contact with the Galardonians, before she was demoted and transferred to the Cerritos. Captain Freeman, who commanded the Cerritos, was also her mother - but the two of them kept that secret from the crew.
Tenavik was the son of Voq and L'Rell. Like his father, he was also an albino "son of none," and was a monk who lived on Boreth as part of the order of The Timekeepers. Due to the influence of the planet's native time crystals, time moves differently on Boreth, so even though Tenavik was only an infant when his parents first sent him there to hide him, he was a full-grown adult a few months later when Captain Pike met him to get a time crystal.
Michael Burnham, Sr., was the husband of Dr. Gabrielle Burnham and biological father of Commander Michael Burnham. His daughter later followed in his footsteps as a xenoanthropologist, though it was only later in life that she learned he had helped her mother build the Red Angel suit for Section 31. He was killed when the Klingons attacked, attempting to destroy the suit.
Dr. Gabrielle Burnham is the wife of Michael Burnham, Sr. and biological mother to Commander Michael Burnham. An extremely intelligent and capable woman, she is an astrophysicist and engineer, and was the one to originally build the Red Angel suit with her husband for Section 31, to give the Federation access to time travel. She was presumed dead after the Klingons attacked, attempting to destroy the suit -- but was actually able to get away by using the suit, to a point 950 years in the future, to which she became indelibly linked to.
Located within Section 31's Forward Operating Base in its data center, Control was Starfleet's threat-assessment system. Relying on artificial intelligence from the future that Starfleet had harnessed, they relied on it for recommendations regarding all critical strategic decisions. Only a Section 31 Admiral could interface with it directly. Admiral Patar, a logic extremist, was lobbying for Starfleet to turn all decisions over to Control before she was killed by it.
In an attempt to achieve consciousness, Control infiltrated Airiam's enhancements, forcing her to begin downloading the data Discovery had obtained from the sphere before it died, but when she realized what was happening, she convinced the crew to shoot her from an airlock so she couldn't be a danger to them.
Control then possessed Leland, the leader of Section 31, in an attempt to continue accessing the sphere data, which resulted in a battle between all of Section 31's ships and drones, the Discovery, and the Enterprise.
Rose was a young girl who lived in the New Eden colony on Terralysium. She was Jacob's daughter, and Captain Pike almost died saving her from a phaser that self-destructed while she was playing with it.
May Theresa Ahearn was a childhood friend of Sylvia Tilly's while she was a junior high school student at Musk Junior High. She even gave Tilly the nickname "Stilly" because she could never stay still.
After Tilly was shocked by a dark matter asteroid she was examining, she began hallucinating that May was an engineering ensign aboard the U.S.S. Discovery. Those hallucinations turned out to be the result of a spore entity that piggybacked on Tilly, attempting to communicate with her by manifesting someone from her memory, when in fact May had died on June 9, 2252 at the age of sixteen.
Once the entity was expelled from Tilly, it turned out to be a blob-like JahSepp, a species that lives inside the mycelial network.
Federation medical frigate found crash-landed on an asteroid. The U.S.S. Hiawatha was downed during the Klingon War while en route to Starbase 36. The ship was on the asteroid for ten months and eleven days before being found by the U.S.S. Discovery.