Walter Ray Allen Jr. (born July 20, 1975) is an American former professional basketball player. He played 18 seasons in the National Basketball Association (NBA) and was inducted into the Naismith Memorial Basketball Hall of Fame as a player in 2018. Allen is widely considered to be one of the greatest three-point shooters of all-time, and he held the record for most three-pointers made in a career from 2011 until 2021, when he was surpassed by Stephen Curry.

On June 28, 2007, the Sonics traded Allen and Glen Davis, the 35th overall pick in the 2007 NBA draft, to the Celtics in exchange for Delonte West, Wally Szczerbiak, and the fifth overall pick, Jeff Green. Shortly after acquiring Allen, the Celtics acquired Minnesota Timberwolves forward Kevin Garnett to play alongside Allen and Paul Pierce. Upon joining the Celtics, Allen changed his jersey to number 20 because Paul Pierce already had number 34 in Boston.