Detective based in Denver, Colorado. Pete met Samantha Carter while on a case in Colorado Springs, after his friend Mark Carter (Sam's brother) set them up. Shortly afterward Pete and Sam began a romantic relationship.
Pete has had a tumultuous past, and thinks that he probably would have ended up in jail if it had not been a particular cop who made a difference in his life. That's part of why he entered this line of work. Pete was previously married, but his wife found his job too difficult a lifestyle to be involved with and subsequently divorced him. He never blamed her for her decision, as the hours of his job are never certain and, all in all, it is a difficult lifestyle to lead while married.
Inquisitive about Carter's true work (beyond deep space telemetry) deep inside Cheyenne Mountain, Pete made a call to F.B.I. agent David Farrity to run a background check on the major. He learned that she was likely involved in top-security work for the government. To try and learn more about what it is Sam really does, Pete followed her on a stake-out and discovered a glowing-eyed woman with a "laser ring" -- Osiris, a Goa'uld who was probing Daniel Jackson's mind while he slept at night. Pete took a hit in the fire-fight that ensued, but survived.
Because of what he had seen, Carter was given permission to disclose to Pete the true nature of the Stargate program and her work there.
During her imprisonment Samantha found herself living on a farm with Pete and raising horses, but, despite Pete's explanation that she had been ill, she soon realized that "Pete" was actually Fifth playing mind games with her.
Pete puts in for a transfer to Colorado Springs and proposes to Sam. He is then called on to use his skills as a detective to discover if Teal'c was responsible for the murder of Doug McNair. Following an operation against the Trust's operatives, Sam finally agreed to marry Pete.
Some time later Sam takes the opportunity of her father being on Earth to introduce Pete to Jacob Carter. Pete was caught out by the surprise meeting and overwhelmed at meeting the host of an alien being and his future Father-in-law. Soon Pete had a surprise of his own. He took Samantha to see the new family house he had just bought for them. Sam, however, was having second thoughts and, shortly after the death of her father, she told Pete that she couldn't marry him.
BEHIND THE SCENES
David DeLuise is the younger brother of long-time Stargate director Peter DeLuise. Actor Ben Browder was offered the role of Pete but declined. (Browder would later appear as Colonel Cameron Mitchell in the final two years of SG-1.)
Chimera - Pete Shanahan continues an intimate relationship with Samantha Carter, and goes behind her back to determine that her real job is traveling to other planets and battling intergalactic villains.
New Order, Part 2 - Fifth uses Pete's likeness to try and trick Sam.
Affinity - Pete asks Sam to marry him, then assists in a murder investigation where Teal'c is the main suspect.
Threads - Samantha Carter ends her engagement to Pete.