It's Thel 'Vadamee. And as of the Great Schism in 2552, the Sangheili have dropped the 'ee' suffix. So it'd be Thel 'Vadam. Before taking on the role of the Arbiter, he was a part of a Zealot team used directly by the Prophet of Regret. After his success at the Rubble, he was promoted to Shipmaster, and given command of a ship in the Fleet of Particular Justice. There, he quickly rose to the rank of Fleetmaster, and soon after Supreme Commander. He is responsible for the deaths of approximately 1.5 billion humans, and the destruction of Reach. Were it not for the failure at Halo being pinned on him, he would have gone on to destroy Earth. As for an honorable opponent, he was obviously noted for allowing an entire company to finish gearing up before slaughtering them.