Kurt-051, born Kurt Trevelyan and later known as Kurt Ambrose, was a Spartan-II super-soldier and later Spartan-III program training lead. He was Green Team lead soon after the Spartan-IIs saw active service, and later took a position with Blue Team. Kurt’s ability to sense danger served to save Blue Team during the Raid on Camp New Hope, which had been staged in order to capture Spartan-IIs for the insurrection. Soon after, the Office of Naval Intelligence sent Blue Team along with Kurt on a mission designed to remove Kurt from active duty while giving the appearance that Kurt was missing in action. ONI used Kurt to head the training program for the new Spartan-III program, as he was considered the best candidate for the job.
Kurt took the surname of Ambrose while training the Spartan-IIIs, spending the next twenty-one years on Onyx training three companies in total. Soon after the completion of Gamma Company’s augmentations and deployments, the entire planet of Onyx was revealed to be a Forerunner shield world, having been activated by the placing of Delta Halo into standby status during the Battle of Installation 05. Kurt, along with several other Spartans, Doctor Catherine Halsey, and Franklin Mendez, set to stop the Forerunner attack, only to find a slipspace rift at the core of the planet. While they successfully found an entrance through the rift into a Dyson sphere known as the Sarcophagus, Kurt stayed behind and gave his life to defend the rift from Covenant forces until it fully closed.