The O'Brien Trophy is a retired trophy that was awarded in the National Hockey Association and the National Hockey League ice hockey leagues of North America from 1910 to 1950. It was originally donated to the NHA by Canadian Senator M.J. O'Brien in honor of his son, Ambrose O'Brien, and has been awarded under four definitions: from the 1910 to 1916–17 NHA seasons, it was awarded to the NHA champion; for the 1917–18 season, the trophy was purchased by the NHL and awarded to the NHL playoff champion until 1923 after which it was retired; for the 1927–28 season, it was reactivated and awarded to the Canadian Division Champion until 1938; and starting with the 1938–39 season, it was awarded to the NHL Playoff Runner-Up. In 1950, the trophy was retired for a second time and has not been awarde