Isaiah Jamar Thomas (born February 7, 1989) is an American professional basketball player for the Phoenix Suns of the National Basketball Association (NBA). He most notably played with the Boston Celtics from 2015 through 2017, when he was a two-time NBA All-Star and named second-team All-NBA.

The 5-foot-9-inch (1.75 m) point guard played three years of college basketball for the Washington Huskies and was a three-time all-conference selection in the Pac-10. After electing to forgo his senior year of college, Thomas was selected by the Sacramento Kings with the final pick in the 2011 NBA draft. He spent three seasons with the Kings before joining the Phoenix Suns in 2014. Thomas was traded to Boston in February 2015. In the 2016–17 season, he led the Celtics to the first seed of the Eastern Conference, had the third-highest points-per-game average in the league, and finished fifth in MVP voting.

After injuring his right hip during the 2016–2017 season, Thomas was traded to the Cleveland Cavaliers in August 2017. Over the next several seasons, Thomas's hip injury significantly hampered his play. Thomas went on to play for the Los Angeles Lakers, the Denver Nuggets, the Washington Wizards, the New Orleans Pelicans, the Dallas Mavericks, the Grand Rapids Gold of the NBA G League, the Charlotte Hornets, and the Salt Lake City Stars.