Thel 'Vadamee is the Supreme Commander of the CAS-class Assault Carrier Seeker of Truth in the Fleet of Particular Justice. He would've been the deuteragonist for the cut levels The Commander and The Commander: Evolved.
Life as Supreme Commander
At some point between 2535 and 2552, Thel's exceptional leadership and combat prowess earned him the rank of the Fleet of Particular Justice's Supreme Commander. During his time as a Supreme Commander, Thel was responsible for over 1 billion human casualties, the loss of at least 7 human worlds, the destruction of over 123 human vessels during fleet action and the deaths of over 23,000 UNSC personnel.
He led the victorious Covenant forces at the Fall of Reach. As the battle ended, Thel ordered all ships within his command to follow the fleeing UNSC Pillar of Autumn. Following the Autumn's course led them to Installation 04. Commanding the Seeker of Truth, he had his ships begin evacuation of the ring upon the release of the Flood, but the parasite managed to capture a ship and infect a Minor Prophet, the Minister of Etiology. The sudden widespread evacuation led to confusion as ships became infested, and he was unable to prevent the destruction of the ring and was forced to abandon it.
The Commander level was a spinoff of Halo SPV3 where the player controls Thel 'Vadamee to fight the Sentinels and the Flood. The Flood would have taken control of the Cartographer to learn more about Installation 04 and how to escape it. It would've been revealed that the Cartographer was not a map room, but a monitoring room where the Flood was figuring how to get around to places. He would've mostly been restricted to Covenant weapons and the Energy Sword would've been an armor ability.