From Halopedia, the Halo wiki
Covenant Empire (formerly)
Monn I'zar was a Sangheili who served in the Covenant's military. Monn did not believe the stories told of the prowess of Spartan-IIs on the field of battle, until he came face-to-face with the Demon himself at some point after July of 2557.
John-117 and Monn I'zar face off against one another.