Right now Dr. Schuster is a brain in a jar.
Dr. Schuster was a neurologist working for Mendat Laboratories when there was an accident. The accident left him with no body but an enlarged brain. He was placed in a jar to keep him alive. Shortly afterword it was discovered he had psychic powers. He was kept in the lab for further study.
American Eagle is currently working on a better way to house the Doctor.
Dr. Schuster recently worked with SYBIL and seems to have a connection with her.
UPDATE: Echo Sheikman has built a robotic body for Dr. Schuster. She is working with him to refine the body, but has also integrated the Doctor with SYBIL. The two are seamlessly working together to improve his control over the body.
UPDATE: Dr. Schuster was one of the Guardians who lost memories when the rest of the team destroyed The Foundry underwater headquarters. He forgot about his tranformation into just a brain, which traumatized him. He fled the team HQ, and was consoled by Princess. He has regained his memories and returned to the team HQ, but is a little more quiet.
Dr. Schuster can communicate telepathically with anyone he has met across the globe. He also has some low level telekinesis.