So, who is everyone’s favorite characters from the extended universe?
Mine are definitely Kilo-five! Amazing team, with a killer leader (I mean, she is CINCONI, so literally a killer) and an awesome AI (BB).
I love Kurt-051, he’ll always be my top favorite. No surprise that I also love all the S-IIIs. 
Before he came into the games, it was Fred, I always loved the knives. Now, it has to be the Elite from the Return.
Ash, Fellow Gamma Spartan III
George Washington…hahaha ok while he is canon, I joke XD. In all seriousness, probably the Primordial. Being the last Precursor and the First Gravemind and still living on in the Flood makes him one of the oldest characters in the franchise.
Probably Gray Team. I liked that they operated deep behind enemy lines without support for years at a time. Kurt is also a character that I like, but unfortunately he worked for ONI, which I have come to despise ever since 343 took over and decided to make that sanctimonious backstabbing organization the center of Halo universe.
Possable Dev from Kilo 5, Kurt-051, or that crazy dude for Hunt The Truth, he was funny af.