The people of the planet Xahea, whose young queen Po befriended Sylvia Tilly and invented a way to recrystallise dilithium.
The Xaheans are the people of the planet Xahea, which was not a member of the Federation in the 2250s. The best known Xahean is Me Hani Ika Hali Ka Po, usually called Po, a brilliant young engineer who is the heir to the throne.
In the Short Treks episode Runaway, Po stows away aboard the USS Discovery, where Ensign Sylvia Tilly finds her. Po explains that she discovered dilithium on Xahea and invented a way to recrystallise it, and that she fled because she did not feel ready to rule and feared what others would do with her discovery. Tilly encourages her to face her responsibilities, and Po returns home to take her place as queen.
Po returns in Discovery's second season finale, Such Sweet Sorrow. As queen, she uses her knowledge of dilithium to help recharge the time crystal that powers Michael Burnham's Red Angel suit, making it possible for Discovery to escape into the future.