Check your titles in the Play Game -> Dog Tags menu. Titles are unlocked by performing in-game challenges. The rank of a title is denoted by the number of stars you see underneath them. The more you do a challenge, the more stars you get for it with a maximum of four.
You should earn quite a few four star titles just by playing through the game normally. An easy one to go for is something like walking distance. Once you’ve earned a four star title you’ll unlock this achievement the next time you visit the dog tags menu.
You can find a list of titles and their requirements provided by X360A user BounTyHunteRZero HERE.