Cassus Fett

Mandalorian warrior and outlaw from the Old Republic, with black armor and silver highlight, who lived during the Mandalorian Wars right before KOTOR

Right hand man to Mandalore the Ultimate.

He was very briefly mentioned in Knights of the Old Republic -- you can obtain his armor and pistol:

Cassus Fett's Heavy Blaster Pistol

Korriban: Talk to the merchant behind the desk near where you meet Lashowe. Ask to see his stock to find Fett's Heavy Blaster pistol. This pistol will be available at any time.
Damage 13-15 (with minor upgrades)
Price: 10000
On Hit: 25% chance to stun for 6 secs.

Cassus Fett's Armor

Dantooine Courtyard: When you get to the third Jedi trial, you will see a merchant near where the Kath Hounds first ambush you. Talk to the merchant that sells armor and weapons. Ask to see his stock and you will see Cassus Fett's Armor. It costs 15,000 credits. Note: You will no longer be able to get the armor after you are taken prisoner by Saul.
Defence: 10
Price: 15000
Resist cold, sonic, and heat 10 pts each

Relative of Boba Fett?

If Cassus Fett has two sons, and if these two sons have two other sons each after 25 years, and if each of these four get two sons after another 25 years, then that would make ... after 4000 years ... 160 generations ... It would mean that all those clone troopers you see in the second prequel are not clones of Jango Fett, but his cousins. A nice little family reunion.
-- GreenTwilek, BioWare KotOR Forum

References