"Tyler" had been taken into captivity by Jaffa troops to be returned for study to unlock his secrets. He managed to escape his prison and crash the transport vessel on a planet, where he escaped and encountered SG-1. In moments he had fully integrated a month's worth of memories with him into their minds, sufficient for hiding out until he had entirely evaded the Jaffa.
Unfortunately, Tyler and Jack O'Neill became pinned down, and General Hammond, who had never heard of Tyler, believed SG-1 might have been compromised. It was only after several days of hiding that Tyler revealed what he truly was, and when the remaining members of SG-1 were allowed to return, Tyler made a run from the foot soldiers to give the team a chance to escape. Teal'c procured a glider cannon and wiped out the troops that swiftly captured him, allowing Tyler to travel through the Stargate to a world the Reole had designated safe haven from the Goa'uld.
Tyler's projected image bears a striking resemblance to Nelson, another person impersonating a member of the S.G.C.. While there is no evidence that the Reole have any telepathic abilities it is possible that SG-1's image of Lt. Tyler originated from their memories of Nelson.
The Fifth Man - An escaped Reole takes on the persona of a human male named Tyler, the fifth member of SG-1, on a training mission.