Jack Sheridan was a mortal co-worker of Prue Halliwell at Buckland's Auction House. He was Prue's first serious love interest after the death of Andy Trudeau.
History
Jack was originally an Internet auctioneer. When Prue was doing a live appraisal for an exquisite wand, Jack muscled in and boldly offered to guarantee the customer $1,000 in cash on the spot. As it turned out, the wand belonged to Tuatha, a powerful evil witch from the 18th century. After Tuatha's defeat, Prue gave the wand back to Jack; the crystal was now broken from using its magic. Jack liked Prue's spunk, and bought her a drink.
Jack liked Prue enough that he convinced his twin brother, Jeff, to help check her out—a stunt they often pulled when they were younger. One day, Prue saw one of the Sheridans in front of her at the coffee pot, then stepped away to the newsstand and found the other one there reading a magazine. This initially led Prue to suspect Jack was a warlock; she didn't think it was possible to go from one place to another that quickly without blinking. To be certain, she and Piper (who suspected Dan was a warlock as well) cast a spell to hear people's thoughts. After Jeff, posing as Jack, showed up later, his thoughts horrified Prue enough that she was initially determined to kill him. However, after the two showed up at the same time, and Jeff says that he works in a mortuary, Prue was convinced they were clean—but slapped them both as punishment.
Soon afterward, Jack decided to accept a long-standing offer to work at Buckland's. He helped Prue close a sale with a Japanese client, using his fluent Japanese to close the deal. He allayed Prue's initial concerns about his ethics by letting her take the credit. Soon afterward, the two started dating.
After dating awhile, Jack planned to take Prue to New York, but Prue backed out when a magical emergency intervened. Their relationship ended soon afterward, though, when Jack wanted to pass off a painting as a Monet. Prue was unwilling to go along, and not only broke off the relationship, but resigned from Buckland's.
Appearances
Jack Sheridan appeared in a total of 7 episodes throughout the course of the series.