Zack Adam Kassian (born January 24, 1991) is a Canadian former professional ice hockey winger. He most recently played for HC Sparta Praha in the Czech Extraliga. During his major junior career, he won a Memorial Cup with the Windsor Spitfires of the Ontario Hockey League (OHL) in 2010. Selected in the first round, 13th overall, by the Buffalo Sabres of the National Hockey League (NHL) in the 2009 NHL Entry Draft, Kassian began his career within the Sabres organization before being traded to the Vancouver Canucks in 2012. He played parts of four seasons with the Canucks before being dealt to the Montreal Canadiens in 2015. Kassian never played for the Canadiens, however, as he was suspended for substance abuse issues, and was moved to the Edmonton Oilers several months later. After seven seasons in Edmonton, Kassian was traded yet again to the Arizona Coyotes, spending one season there before retiring from NHL play during the 2023–24 season.

Internationally, he competed with Canada's under-20 team at the 2011 World Junior Championships and won a silver medal. Listed at 6 ft 3 in (191 cm) and 211 lb (96 kg), Kassian played in the style of a power forward and was known for playing with aggression and physicality.

Kassian was born in Windsor, Ontario, to parents Mike and Shirley Kassian. Though often mistaken for having Armenian heritage, Kassian is not of Armenian descent. He has two older sisters and an older brother, Mike Jr. When he was eight, his father died of a heart attack. Kassian has recalled his father's role as having been filled by Mike Jr., who was nineteen at the time, while he grew up. He grew up attending Queen of Peace elementary school in Leamington, Ontario and first began playing organized hockey at the age of eight with the Kingsville Kings. Growing up, he was a Toronto Maple Leafs fan, though he has listed his favourite players as Boston Bruins defenceman Bobby Orr and Todd Bertuzzi, a fellow power forward who was starring with the Vancouver Canucks during Kassian's youth.

After a season of AAA midget with the Windsor Jr. Spitfires, Kassian debuted at the major junior level with the Peterborough Petes in 2007–08. Playing in his first career OHL game, he recorded two assists against the Sudbury Wolves on September 20, 2007. He scored his first OHL goal the following month against the Erie Otters on October 11. He went on to score 9 goals and 21 points over 58 games as a rookie. In the following season, he improved to 24 goals and 63 points over 61 games. He also had a team-leading 136 penalty minutes and earned a reputation as a willing fighter with 13 fighting majors. That season, he was chosen to play in three All-Star exhibitions. Near the beginning of the campaign, he represented Team OHL in two games against a select team of Russian juniors, as part of the annual Subway Super Series. Kassian later dressed for the Eastern Conference in the OHL All-Star Classic and scored a goal and an assist. Lastly, he competed in the 2009 CHL Top Prospects Game for Team Cherry, a contest in which he injured John Tavares with a hit.

Leading up to the 2009 NHL Entry Draft, Kassian was ranked 10th among eligible prospects playing in North America (not including goaltenders) by the NHL Central Scouting Bureau (CSB). Chris Edwards of the CSB heralded him as "one of the toughest guys in the OHL and probably the entire draft", while also highlighting his "play-making and puck-handling abilities". Scouted as a power forward, he was compared to such players as Milan Lucic, as well as retired NHL All-Stars Cam Neely and Keith Tkachuk.^{[citation needed]} Kassian went on to be selected in the first round, 13th overall, by the Buffalo Sabres in the draft.

Kassian went on to attend his first NHL training camp in September 2009 and was returned to Peterborough to continue at the junior level. Back with the Petes, Kassian was chosen to replace the departed Zach Harnden as team captain after Harnden starting playing with the Kingston Frontenacs. Thirty-three games into his 2009–10 OHL season, Kassian was traded to the Windsor Spitfires. Before the trade, Kassian had been suspended one game by his team for breaking curfew. Shortly after joining Windsor, he was given a 20-game suspension from the league for his hit to the head of Barrie Colts forward Matt Kennedy during a game in January 2010. Limited to 38 games between Peterborough and Windsor due to the ban, Kassian totalled 12 goals and 31 points. Returning from the suspension in time for the 2010 playoffs, he added 7 goals and 16 points over 19 games to help Windsor to a J. Ross Robertson Cup as OHL champions. The win qualified Windsor for the 2010 Memorial Cup, Canada's national major junior championship, which they won as well. Defeating the Brandon Wheat Kings in the final 9–1, Kassian had a goal and an assist in the championship-winning game.

Following the Memorial Cup win, Kassian was arrested after an altercation at a bar in Downtown Windsor on May 30, 2010. Charged with assault, he reached an agreement several months later, in October 2010. The charge was dropped in exchange for 25 hours of community service, a $500 donation to charity, and payment for the victim's dental work. Had he been convicted, Kassian would have been ineligible to cross the border into the United States, which would have conflicted with his hockey career.

Kassian returned to the Sabres' training camp in September 2010. While he was sent back to junior for the second straight year, he remained on the team's pre-season roster as one of the final cuts in October. A month after being returned to Windsor, he signed a three-year, entry-level contract with the Sabres on November 2, 2010. Playing his first full season with Windsor, Kassian recorded a junior career-high 26 goals and 77 points over 56 games. His points total ranked second in team scoring, behind captain Ryan Ellis' 100. He then added 16 points (6 goals and 10 assists) over 16 OHL playoff games, tying for fifth in team scoring. During Game 4 of the Conference Finals against the Owen Sound Attack, Kassian received a match penalty for a hit on opposing defenceman Jesse Blacker, which was ruled as "intent to injure". Following the contest, the penalty was supplemented with an additional three-game suspension, sidelining him for the remainder of the series. Out of the lineup for Game 5, he only needed to serve half of the total suspension as the Attack eliminated the Spitfires four-games-to-one.