Regan Matthews was a LuthorCorp executive who worked closely with Lex Luthor while he was investigating the Veritas Society. When Tess Mercer took control over LuthorCorp in Summer of 2008, Regan went missing after he had temporary control and instead began working secretly with Lex Luthor on a new project called Prometheus.
Regan Matthews didn't like Tess Mercer; in fact he seemed to get annoyed or angry whenever they were together.
When Lex was about to go to Zurich to open the box after he had obtained the two Veritas keys, Regan came into his office at the Luthor Mansion to tell him that the government had denied him flight clearance to leave America.
When Jimmy wanted to back out of the deal he made with Lex over Chloe's freedom, Regan escorted him to the Daily Planet and back out again. He also advised Lex about going to the Arctic after reporting that the two LuthorCorp teams were missing. He then went with Lex to the arctic on the LuthorCorp jet.
Regan was temporarily in charge of LuthorCorp after Lex went missing and was heading the Arctic search team. Tess Mercer arrived via helicopter and assumed control by Lex's written instructions. He then went to the Black Creek facility and forced Chloe (with Chloe's super intelligence from the attack of Brainiac) to decipher the last phone number of Green Arrow using a mind control serum taken from Moira Sullivan's spinal fluid. Once he located Green Arrow, Regan controlled him with the same serum, which led to Oliver shooting a powerless Clark Kent with an arrow.
Regan returned and Tess spoke with him in her car, to gain information about Project Prometheus, which he refused to divulge and also after he rejected her job offer in favor of staying loyal to Lex. When she returned to the Planet, Reagan was there to prevent her from getting more information about Prometheus by killing her messenger. When he tried to kill her, Tess beat Regan, by knocking him out with a trophy and then, she began kicking him repeatedly.
However, Tess did not kill Regan. Much later, Lois saw a video of Tess interrogating Regan about the Orb.