Canderous Ordo is a Mandalorian of Clan Ordo who fought through the Mandalorian Wars with the Neo-Crusaders under Mandalore the Ultimate, was decisively beaten by Republic forces under Revan, and surrendered his weapons with everyone else. When the player meets him he is a mercenary on Taris doing enforcement work for a local crime boss, and thoroughly bored.
What the character is for
He is the first Mandalorian in Star Wars fiction to be written from the inside at length — not a bounty hunter in armour but a man from a culture, articulating what that culture thinks it is for and why losing a war nearly ended it. Almost everything later writers do with Mandalorian identity, up to and including The Mandalorian, is downstream of the vocabulary these games established.
Mandalore the Preserver
By Knights of the Old Republic II: The Sith Lords (2004) he wears the mask himself, credited simply as "Mandalore," and is gathering the scattered clans on Dxun. The title he takes — the Preserver — is the point: his war leader was called the Ultimate and led them to annihilation.
Behind the scenes
He was voiced by John Cygan in both games and written for the sequel by Michael Chu. He, Mission Vao, Carth Onasi and Bastila Shan all grew out of James Ohlen's earlier tabletop campaigns for West End Games.