Simon Klein was a UNSC spy during Operation: TREBUCHET.
Simon was born on Erianus II, his parents sent him away to serve in the UNSC army for two years.
Klein found himself mixed into the Insurection, but still felt loyal to the UNSC. He was contacted by the UNSC in 2511 and informed on movement and locations, as well as events to the UNSC. He was even trusted by Elizabeth Knight.
After an attempted assassination in 2524 by Spartan Legacy Team, Simon was revealed to be a spy, after a short hand-hand fight between Simon and Elizabeth. September 17 that same year, Knight personally and publically executed him.