Bo-Katan appeared in The Mandalorian season 2, episode 3 and brought Clan Kryze into live-action, but in doing so, she might've confirmed a Clone Wars character's death. One of the best things about Disney's era of Star Wars is seeing animated characters come to life; this was notably done with Forest Whitaker's Saw Gerrera in Rogue One: A Star Wars Story and now it's been done on an arguably bigger scale with Bo-Katan (Katee Sackhoff) - who originally appeared in Clone Wars and Star Wars Rebels - in The Mandalorian.
Decades before the events of The Mandalorian, Bo-Katan and her Nite Owls fought alongside Death Watch and the Shadow Collective against the Duchess of Mandalore, Satine Kryze (Bo-Katan's sister). The Duchess was the leader of the New Mandalorians during the Clone Wars and she was grooming her nephew, Korkie Kryze, to one day take over for her and lead Mandalore in a new direction, one that disavowed the ancient, bellicose traditions Mandalorians were known for. Korkie never got the chance to do that because Mandalore had been occupied by Maul during the Clone Wars and then later the Imperials during the Age of the Empire.
It's never been revealed who Korkie's parents were, though the prevailing theory among fans is that he was Satine and Obi-Wan Kenobi's secret child (Clone Wars did tease a past relationship between them, after all). The only thing known about his origins is that he's Satine and Bo-Katan's nephew, which doesn't bode well for him considering Bo-Katan told Din Djarin in The Mandalorian season 2, episode 3 that she was the last of her line. Clone Wars fans know Satine was executed by Maul - in front of Obi-Wan, no less - during the Clone Wars, but Korkie's whereabouts have been up in the air.
The last time Korkie was seen on-screen was in Clone Wars season 5, episode 16, "The Lawless", which saw Korkie align with Bo-Katan in an attempt to rescue Satine from Maul and the Shadow Collective. The rescue attempt failed and Satine was killed, but Korkie disappeared and was never heard from again. Given that he's one of only three known members of Clan Kryze, and one of them was killed on-screen, it's safe to assume he died at some point during the Empire's reign.
Like his aunt Satine, Korkie was profoundly patriotic and wanted nothing more than a better future for Mandalore. If he was still alive, his name should've come up in Star Wars Rebels when Sabine Wren returned to Mandalore - but it didn't. And now that Bo-Katan says she's the last of her line, it stands to reason either Korkie went so deep into hiding that his own aunt doesn't know he's alive, or that he was killed, presumably by the Empire. Hopefully The Mandalorian provides a solid answer if and when Bo-Katan shows up again.