Karl Alzner (born September 24, 1988) is a Canadian professional ice hockey defenceman, currently playing for the Laval Rocket of the American Hockey League (AHL) while under contract to the Montreal Canadiens of the National Hockey League (NHL). He was drafted in the first round, fifth overall, by the Washington Capitals in the 2007 NHL Entry Draft. A standout in junior with the Calgary Hitmen of the WHL, Alzner won two World Junior Hockey Championship gold medals with Team Canada 2007 and 2008 (as the captain). Alzner was named the Western Hockey League (WHL)'s top player and Canadian Hockey League (CHL)'s top defenceman in 2008. He won back to back Calder Cups and won the Presidents' Trophy in 2016 and 2017 with the Washington Capitals.