Jacob Muzzin (born February 21, 1989) is a Canadian former professional ice hockey defenceman and current member of the Player Development department for the Toronto Maple Leafs of the National Hockey League (NHL). He previously had played 12 seasons in the NHL for the Los Angeles Kings and Maple Leafs. Originally drafted by the Pittsburgh Penguins in the 2007 NHL Entry Draft, Muzzin went unsigned and returned to the Sault Ste. Marie Greyhounds of the Ontario Hockey League (OHL) as an overage player. There he served as team captain and won the Max Kaminsky Trophy as the top defenceman in the OHL. As a free agent, Muzzin signed with the Kings in 2010, winning a Stanley Cup with the team in 2014. Muzzin was traded to Toronto during the 2018–19 season, where he played parts of five seasons. After a spinal injury suffered in 2022 resulted in his placement on long-term injured reserve, Muzzin joined the Maple Leafs' front office as a professional scout in 2023.

Internationally, he represented Canada at the 2015 IIHF World Championship and 2016 World Cup of Hockey, winning gold in both tournaments.

Muzzin played his early minor hockey in the Woodstock Minor Hockey Association before moving on to play AAA in Brantford, Ontario. He had previously played both soccer and hockey but at the age of 13 he committed to hockey.

Muzzin was the first pick, 11th overall, by the Sault Ste. Marie Greyhounds of the Ontario Hockey League (OHL) in the 2005 OHL Priority Selection Draft from the Brantford 99'ers Minor Midgets. He did not play with the Greyhounds until late in 2006 after he required herniated disc surgery at age 16. Despite having played only 37 regular season games and 13 playoff games, he was drafted 141st overall in the 2007 NHL Entry Draft by the Pittsburgh Penguins. Although he was drafted, he went unsigned by the Penguins and re-entered the 2009 NHL Entry Draft but was not picked and returned for an overage year with the Greyhounds. In his final season in the OHL, Muzzin was named team captain and selected for the 2010 OHL All-Star Classic. Muzzin also won the Max Kaminsky Trophy for top defenceman in the league.

Muzzin signed as a free agent to a three-year, entry-level contract with the Los Angeles Kings on January 4, 2010.

Following the Kings' training camp and pre-season games, Muzzin made the Kings' opening night roster for the 2010–11 season. However, on November 3, 2010, he was assigned to the Kings' American Hockey League (AHL) affiliate, the Manchester Monarchs. Just six days later, on November 9, the Kings recalled Muzzin for a brief stint before again reassigning him to the Monarchs on November 23.

In 2012, Muzzin was recalled during the 2012 Stanley Cup playoffs as a Black Ace, and was on the roster as a healthy scratch when they won the Stanley Cup over the New Jersey Devils. He did not appear in any games that season. Although he did not qualify to have his name engraved on the Stanley Cup, he was nonetheless included in the team's celebratory picture.

Muzzin scored his first NHL goal in his third game following the 2012–13 NHL lockout on January 26, 2013, against Jason LaBarbera of the Phoenix Coyotes. He went on to become a regular in the Kings' lineup and scored 7 goals and 9 assists in 45 regular season games, while adding 3 assists in 17 playoff games. He was also named NHL Rookie of the Month for March 2013.