Bo-Katan, the Mandalorian leader from the Star Wars: The Clone Wars, appears in live-action in season two, first encountering Din Djarin when she and other Mandalorians rescue him and Grogu from some baddies. She's got one major goal in mind: reclaiming the Darksaber — which Moff Gideon has — and restoring Mandalore. In pursuit of that, she agrees to help Din rescue Grogu from Moff Gideon, on the condition that she be the one to take down Gideon and take his ship and saber.
Unfortunately, things go sideways, and Din is forced to fight Gideon one-on-one. Din wins and brings Gideon and the Darksaber to Bo-Katan, but Gideon reveals something Din didn't know: the Darksaber only can fulfil its real power when it's won in battle, meaning that Bo-Katan cannot wield it — it belongs to Din now.
(And yes, this is an animated image from The Clone Wars, as Disney has not supplied any pictures of Bo from The Mandalorian.)