From Halopedia, the Halo wiki
Magnus was an Orbital Drop Shock Trooper sniper assigned to the UNSC Midsummer Night.
In 2535 he landed in the Scyllion Warehouse District on Charybdis IX to break up an Insurrectionist riot led by Jason Kincaide. Magnus and another ODST sniper, Jeremy, killed several hidden Insurrectionists wielding RPGs who had already killed Jeffries attempting to fly in a Pelican to evacuate the trapped ONI crew and Lieutenant Jacob Keyes on a rooftop. His squad had been dispatched on the planet inside HEVs since air transport was too risky and because of time constraints.