Alex Formenton (born September 13, 1999) is a Canadian professional ice hockey left winger for HC Ambrì-Piotta of the Swiss National League (NL). Formenton has also played for the Ottawa Senators of the National Hockey League (NHL). He won a gold medal with Canada's junior team at the 2018 World Junior Championships. He was selected by the Senators in the second round of the 2017 NHL entry draft. He also won the 2022 Spengler Cup with HC Ambrì-Piotta.

Formenton was born in Barrie, Ontario, on September 13, 1999. Formenton's early years were spent in the York area, and for the 2015–16 season he played for the Aurora Tigers of the Ontario Junior Hockey League. In his childhood, Formenton's mother cared for two adult brothers with autism and Down syndrome. Formenton spent time with them while his mother cared for them. While playing for the London Knights, he billeted with a family that included a girl with Down syndrome. He has attributed these experiences to his desire to "seek out some sort of cause or charity that helps people who have Down syndrome or autism".

Formenton was selected by the London Knights of the Ontario Hockey League (OHL) in the eleventh round, 216th overall, of the 2015 priority draft. Formenton made his major junior hockey debut with the Knights in the 2016–17 season and recorded 16 goals and 18 assists for 34 points in 65 games. Formenton was selected to play in the 2017 CHL Top Prospects Game. The Knights qualified for the 2017 OHL playoffs and advanced to the conference semifinals, losing to the Erie Otters. Formenton went scoreless in 14 playoff games. He returned to London for the 2017–18 season and appeared in 48 games, scoring 29 goals and 48 points. The Knights made the playoffs again, but were knocked out in the first round by the Owen Sound Attack. Formenton tallied five goals and seven points in the four game series.

He returned to London in late November for the 2018–19 season. He recorded 13 goals and 34 points in 31 games. The Knights made the 2019 OHL playoffs and advanced to the conference semifinals only to be eliminated by the Guelph Storm. Formenton added four goals and 18 points in 11 playoff games.

The Ottawa Senators of the National Hockey League (NHL) selected Formenton in the second round, 47th overall, of the 2017 NHL entry draft. Formenton was invited to the Senators' main training camp after attending its development camp in mid 2017. At the end of training camp, Ottawa retained him on its NHL roster to open the 2017–18 season and signed him to a three-year entry-level contract. Formenton made his NHL debut on October 7, 2017, becoming the youngest player to play a game for the contemporary Senators franchise. He was a healthy scratch after that game, and on October 15, he was returned by the Senators to continue his development with the London Knights. After the OHL season ended in 2018, Formenton was reassigned to the Ottawa's American Hockey League (AHL) affiliate, the Belleville Senators. Formenton made two appearances with Belleville.

Formenton earned a spot on the Senators' roster for the 2018–19 season. On October 30, Formenton scored his first career NHL goal against Arizona Coyotes goaltender Antti Raanta, the lone Senators goal in a 5–1 loss. He was returned to London in November after appearing in nine games, scoring the one goal. After making the Senators out of training camp for two straight seasons, but failing to stick with the team for the 2019–20 season, Formenton was assigned to Belleville to help round out his game. Before the season was cancelled due to the COVID-19 pandemic, Formenton scored 27 goals and 53 points in 61 games with Belleville. Formenton was selected to represent Belleville at the 2020 AHL All-Star Classic. He was named to the AHL's All-Rookie Team alongside teammate Josh Norris. In the pandemic-shortened 2020–21 season, Formenton split time between Ottawa and Belleville, recording four goals and six points in 20 games in the NHL and four goals in 13 games in the AHL. Throughout the season, Formenton struggled with the effects of an illness that affected his play.

Formenton played with Ottawa for the 2021–22 season, establishing himself as a solid penalty killer. In November, Formenton contracted COVID-19 and was placed in the NHL's COVID-19 protocol. He finished the season with 18 goals and 32 points in 79 games.

After his contract expired following the 2021–22 season, the Senators and Formenton could not agree to terms on a new contract. Remaining unsigned and later becoming ineligible to appear in the 2022–23 NHL season, Formenton belatedly signed with Swiss club HC Ambrì-Piotta of the National League (NL) on December 14, 2022. HC Ambrì-Piotta later issued a statement saying that their contract with Formenton would be re-evaluated at a later date should an investigation of an alleged 2018 sexual assault by members of the Canadian world junior team, of which Formenton was a member, reveal wrongdoing by the player. Senators General Manager Pierre Dorion did not clarify whether Formenton's contract status with the organization was related to the investigation, though some in the media stated that the investigation into Formenton's involvement was the reason for the contract stalemate. Canadian newspaper The London Free Press noted that it is "ultra-rare" for an NHL team to allow a top prospect like Formenton to be unsigned for an entire season. Heading into the 2023 NHL entry draft it was anticipated that the Senators would trade Formenton's rights to free up a spot on the club's reserve list, but Dorion was unable to find a trading partner.