Joseph Eric Thornton (born July 2, 1979) is a Canadian professional ice hockey centre and alternate captain for the San Jose Sharks of the National Hockey League (NHL). He was drafted by and played seven seasons for the Boston Bruins before being traded to San Jose in 2005–06. He was an Art Ross- and Hart Memorial Trophy-recipient in his first season with the Sharks. Thornton's on-ice vision, strength on the puck, deft passing ability, and power forward style of play have led to him becoming one of the league's premier top line centres.

Joe would play for the St. Thomas Stars Jr. B hockey club of St. Thomas, Ontario, Canada before moving on to the Jr. A level. Thornton played major junior hockey in the Ontario Hockey League (OHL) with the Sault Ste. Marie Greyhounds for two seasons, beginning in 1995–96. He posted a 76-point season as a rookie, earning him the Emms Family Award as the OHL's top first-year player, as well as CHL Rookie of the Year honours. The following season, in 1996–97, Thornton improved to 41 goals and 122 points, second overall in league scoring behind Marc Savard of the Oshawa Generals, and was named to the OHL Second All-Star Team.

After his second OHL season, Thornton was drafted first overall in the 1997 NHL Entry Draft by the Boston Bruins. He made the immediate jump to the NHL from junior, debuting with the Bruins in 1997–98. However, with high expectations, Thornton was made a healthy scratch early in the season and did not score his first NHL goal until December 3, 1997, in a 3–0 win against the Philadelphia Flyers. He completed his rookie campaign managing 7 points in 55 games. The following season, Thornton was able to make a significant impact and improved to 41 points in 81 games, including a 9-point effort in 11 playoff games that post-season. He continued to build as a key player in the Bruins' lineup, culminating in his appointment as team captain in 2002–03, succeeding previous captain Jason Allison who had left for the Los Angeles Kings after the 2000–01 season. Thornton responded with a 101-point season, third in league-scoring, behind Peter Forsberg and Markus Näslund, and his highest output as a Bruin.