Erik Sven Gunnar Karlsson (pronounced [ˈêːrɪk ˈkɑ̌ːɭsɔn]; born 31 May 1990) is a Swedish professional ice hockey player who is a defenceman for the Pittsburgh Penguins of the National Hockey League (NHL). Karlsson was drafted in the first round, 15th overall, by the Ottawa Senators at the 2008 NHL entry draft, with whom he spent his first nine NHL seasons; he has also played for the San Jose Sharks. Karlsson is a three-time winner of the James Norris Memorial Trophy as the NHL's best defenceman, winning the award in 2012, 2015, and 2023.
Karlsson made his Elitserien debut for Frölunda HC on 1 March 2008, recording 8:48 of ice time during a sold out home game in Scandinavium against league leaders HV71. Karlsson scored the game-winning goal, assisted by Tomi Kallio and Magnus Kahnberg, with a slap shot in overtime during a man advantage. The win secured a playoff berth for Frölunda with three games remaining in the regular season.
Karlsson finished the season with Frölunda's J20 team playing in the J20 SuperElit playoffs, where Frölunda took home the Anton Cup when they won, two games to one, against Brynäs IF's J20 team in the Swedish Junior Ice Hockey Championship final.
Prior to the 2008 NHL entry draft, Karlsson was ranked fourth among European skaters by the NHL's Central Scouting Service. He was ultimately drafted 15th overall by the Ottawa Senators in front of their hometown fans at Scotiabank Place in Ottawa. The selection was made by Ottawa's captain Daniel Alfredsson, a native of Gothenburg, who played for Frölunda before entering the NHL. Then-Ottawa general manager Bryan Murray traded Ottawa's first-round pick, 18th overall, and their third-round pick in 2009 to the Nashville Predators in exchange for the Predators' first-round pick, 15th overall, to ensure that no other team would select Karlsson before them.
A few weeks before the 2008–09 Elitserien season premiere, Frölunda announced that Karlsson was brought up to the senior team as a regular roster player.
In September 2009, Karlsson attended the Senators' training camp ahead of the 2009–10 season. On 29 September 2009, the Senators announced that Karlsson had made the team's NHL roster. Karlsson made his NHL debut on 3 October, against the New York Rangers, and recorded his first NHL point, an assist. After struggling in nine regular season games with Ottawa, he was assigned to the team's American Hockey League (AHL) affiliate, the Binghamton Senators. On 27 November 2009, exactly one month after being sent down, Karlsson was recalled from Binghamton. He would score his first NHL goal against the Minnesota Wild's Niklas Bäckström in a 4–1 win for Ottawa on 19 December 2009, and would remain in the NHL for the remainder of the season and play in all of Ottawa's 2010 Stanley Cup playoff games.
Karlsson was selected to participate in the 2011 NHL All-Star Game, set for 30 January 2011, at the RBC Center in Raleigh, North Carolina, having recorded 25 points in 41 games.
The 2011–12 season saw Karlsson continue his development. On 16 December 2011, with his third assist of the night, Karlsson registered his 100th regular-season NHL point (in 168 games) in a game against the rival Pittsburgh Penguins. Karlsson was the NHL's leading vote-getter in All-Star voting, receiving 939,951 fan votes and becoming one of four Senators players selected to partake in the 2012 NHL All-Star Game. Karlsson finished the season as the leading scorer among NHL defencemen, leading second-place Dustin Byfuglien and Brian Campbell by 25 points. Karlsson was being mentioned as a James Norris Memorial Trophy candidate, if not the favourite for the award. During the season he set a new Senators franchise record for points in a season by a defenceman (previously held by Norm Maciver) with 78.
On 19 June 2012, Karlsson signed a reported seven-year, $45.5 million contract with the Senators. The following day, Karlsson was announced as the winner of the James Norris Trophy as the NHL's best defenceman, beating Zdeno Chára of the Boston Bruins and Shea Weber of the Nashville Predators. He became the second Swede after seven-time winner Nicklas Lidström to win the award, joining the ranks of Hall of Famers Bobby Orr and Denis Potvin as the only players to win the award under age 23.
During the 2012–13 NHL lockout, Karlsson signed with Jokerit of the Finnish SM-liiga. He received a one-game suspension for allegedly throwing his stick at a referee following a game on 8 December 2012. He finished his stint in Jokerit with 9 goals and 25 assists (34 points) in 30 games, leading all defencemen in scoring. Once the lockout ended and the season commenced in January 2013, Karlsson promptly recorded a goal and two assists as Ottawa defeated the Winnipeg Jets 4–1 in their season opener. On 13 February 2013, Karlsson's Achilles tendon was lacerated when Pittsburgh Penguins forward Matt Cooke had his skate land on the back of Karlsson's left leg, requiring surgery and taking him out of Ottawa's lineup indefinitely. Cooke had been suspended several times previously for much-criticized incidents resulting in injury to opposing players, but was not suspended for this incident. At the time of the injury, Karlsson led all NHL defencemen with six goals. Though initial estimates had him out of the lineup for four-to-six months, Karlsson returned to the Ottawa lineup against the Washington Capitals on 25 April 2013, ten weeks to the day after the injury occurred. The Senators made the 2013 Stanley Cup playoffs but were eliminated by Pittsburgh in the Eastern Conference semifinals, with Karlsson registering one goal and seven assists in ten games.
Karlsson appeared in all 82 games during the 2013–14 season and finished the season with 20 goals, 54 assists and 74 points, resulting in Karlsson being the first defenceman since Brian Leetch in 2000–01 to have at least 20 goals and 50 assists in the same season. He passed Steve Duchesne for franchise record for most goals in a season by a defenceman with 20. However, the Senators would fail to qualify for the 2014 playoffs.
On 2 October 2014, the Senators organization announced that Karlsson would serve as the ninth captain in the team's modern history, replacing the recently traded Jason Spezza. In his first season as team captain, Karlsson led all NHL defencemen in points for the third time in four seasons, including a career-high 21 goals. He also played in all 82 of Ottawa's games for a consecutive season and ranked third in the NHL in total ice time (2,234:55) and average ice time (27:15) to carry the Senators to a 23–4–4 record on the way to an unlikely playoff spot. On 24 June 2015, it was announced Karlsson won his second Norris Trophy, beating out fellow nominees Drew Doughty and P. K. Subban.
Karlsson appeared in all 82 games for the third-straight season during the 2015–16 season and led the league in assists with a career high 66 assists and set a career high in points (82), finishing fourth in the league in scoring alongside San Jose Sharks forward Joe Thornton. With his 81st point, Karlsson broke the record for most points in a single season by a Swedish defenceman, which was previously set by Nicklas Lidström during the 2005–06 season. Karlsson was also the first defenceman since Paul Coffey in the 1985–86 season to finish in the top five in scoring and the first since Bobby Orr in the 1974–75 season to lead the league in assists. Karlsson's performance earned him his third Norris Trophy nomination, though Drew Doughty won the trophy with Karlsson finishing in second place in vote totals.
During the 2016–17 season, Karlsson set a Senators record on 4 March 2017, when he appeared in his 312th consecutive game, breaking the previous set by defenceman Chris Phillips. However, he would miss his first game in almost four years in late March 2017 after sustaining an injury from blocking a shot during a game against the Philadelphia Flyers, ending his consecutive game streak at 324 games. Karlsson finished the regular season in third place among defencemen in points and second place among defencemen in assists and blocked shots, earning him his fourth Norris Trophy nomination. Karlsson would finish second in voting, with the award going to Brent Burns of the San Jose Sharks. Karlsson's performance continued into the 2017 playoffs, helping the Senators reach the conference finals, the first time the team had done so since 2007. Although the Senators would be eliminated by the Pittsburgh Penguins in seven games losing the deciding seventh game in double overtime, one win and goal short of reaching the 2017 Stanley Cup Final, Karlsson was praised for his performance during the Senators' playoff run and how he continued playing despite suffering two hairline fractures in his left heel. Karlsson would also set a playoff team record for most assists and points for a defenceman in the playoffs, breaking the previous record set by Wade Redden in the 2006 playoffs (eight assists, 10 points). And despite being eliminated in the conference finals, Karlsson received a Conn Smythe Trophy vote without playing a game in the Stanley Cup Final.