Major Marks has served on the crew of both the Prometheus and the Odyssey. On one of his earliest assignments, at the rank of lieutenant, he served aboard the Prometheus during the mission to Glastonbury. From his position in auxiliary control room 2, he used the Asgard sensors to map the energy distortion field that concealed the cavern below Glastonbury Tor. After the discovery of Merlin's treasure, he was among the crew that explored the cavern area, and he discovered the Ancient communication terminal among the artifacts and treasures. On subsequent missions, Marks has served on the bridge, taking a position both to the commander's right and to the left, and his responsibilities have included communications, navigation, sensors, status readings, repairs, transport beaming, and weapons, for which, for the record, he is always prepared.
Aboard the Prometheus, Lieutenant Marks served under Colonel Pendergast during the mission to Kallana to prevent the formation of an Ori supergate and during the mission to search for Ba'al on Earth. Lieutenant Marks was promoted to the rank of captain, and he again served under Colonel Pendergast during the mission to Tegalus. Prometheus intended to destroy the Ori satellite weapon, but the ship was targeted instead, and Captain Marks was among the 76 crew members who beamed to the planet's surface and survived the destruction of Prometheus.
Following the loss of Prometheus, Marks was promoted to the rank of major and assigned to the Odyssey under the command of Colonel Emerson. He served during the ship's shakedown cruise when Odyssey was diverted to rescue SG-1 from the Lucian Alliance on P6G-452, during the battle against the Ori invasion at the supergate, and during the rescue of SG-1 from the activation of the Dakara weapon by the Jaffa High Council. He was also among the crew members taken hostage by Anateo when he captured the Odyssey and killed Colonel Emerson. Afterward, Marks served under Colonel Davidson during Odyssey's mission to locate Arkad's cargo ships intended for the attack on Earth, and when Odyssey acquired Asgard upgrades at Orilla and was pursued by Ori warships on the return voyage, Major Marks and the crew were beamed down to P3X-474 from which they were able to gate back to Earth.
Portrayed by: Martin Christopher