Simmons was born to a Caucasian father and a Korean mother. Because of his mixed ethnicity, his paternal grandparents ostracized him. He and his wife Kristy have four children: two sons Jake and David, and twin toddler girls. This latter fact has caused some jokes about him being a "breeder". He is an FBI agent and specifically works for Jack Garrett and the International Response Team. Through this job, Simmons has some prior history with Derek Morgan and Jennifer "JJ" Jareau. He is a military veteran who has seen combat overseas, presumably the Middle East. This allowed him to hone his split-second decision making skills. Hence, he is usually the quickest of the team to draw up a preliminary profile on the unsub.
Simmons is first seen coming out of the SUV with Jack and Lily Lambert, who are all on their way to the plane. There, they meet up with Morgan and JJ, who learn about Matt's newborn twin daughters. They then board the plane and discuss the case aboard. During the investigation, Simmons is paired up with Morgan and JJ. He delivers the profile along with the other members of the BAU and the International Unit. Afterwards, they look up on the computer and eventually identify the unsub as Jerry Tidwell. The following night, Simmons uses a speedboat to get to Tidwell's boat, where he is holding the Sullivan family captive. After Tidwell is killed and he is informed about the son Nick being thrown overboard, Simmons locates Nick on a small raft, rescues him, and brings him back aboard Tidwell's boat. Back in Quantico, Simmons, along with the others, watch as the Sullivans are reunited with their relatives.
Simmons reappears in the episode, working alongside Clara Seger when they are called in by Prentiss to help Reid, who was arrested in Mexico for drug possession and the murder of Nadie Ramos. At the time, the IRT was investigating another case in Costa Rica. The two IRT agents arrive at the local jail Reid is being held in and try to stop his transfer to Prisión de Máxima Seguridad El Diablo. Simmons tells Reid about a new lead, adding that there is no contraband on him. When Reid asks what were inside the vials of experimental medication he had, Simmons gives him a list of the medication's ingredients. This helps the BAU pinpoint Nadie's hometown. Just then, the Mexican police are given orders to transfer Reid to El Diablo. However, the agents are able to stop the transfer and have him extradited back to the U.S. after they realize the victim has dual American-Mexican citizenship. Afterwards, Simmons is seen onboard the BAU's plane, thanking Rossi for having him and Seger flown back to Quantico.
Criminal Minds: Beyond BordersEdit
Matt is portrayed as the muscle of the team, similar to the role Morgan played on the original show.