The Celtics are sending guard Kemba Walker and their 2021 first-round draft pick to the Oklahoma City Thunder in Brad Stevens' first move in charge of Boston's front office.
The Celtics will also trade a second-round pick in 2025 as part of the package for veteran center Al Horford, young 7-footer Moses Brown and a second-round draft pick in 2023.
The Celtics acquired Walker from the Charlotte Hornets in a trade on July 6, 2019, that sent Terry Rozier to Charlotte. The two also swapped second-round draft picks. Before the trade, Walker signed a four-year, $140.8 million max contract with the Hornets -- with half still due to him. He is the all-time leading scorer in Hornets' franchise history (12,009 points).
Walker struggled with injuries, primarily to his left knee, throughout the 2020-21 season. He was limited to 43 regular-season games and missed the final two games of the Celtics' loss to the Brooklyn Nets in the first round of the playoffs.
"Kemba is a true professional and a great teammate and player," said Stevens, who replaced Danny Ainge as president of basketball operations on June 2.
"I want to thank him for his tremendous impact, and the positive contribution he's made both to the Celtics and the City of Boston."
The trade sends 35-year-old Horford back to Boston, where he played from 2016-19. He was a healthy scratch for Oklahoma City the final 28 games of the season and has two years and $53.5 million remaining on his contract.
Walker, 31, is a four-time All-Star. In 704 career games (659 starts) with the Hornets and Celtics, Walker has averaged 19.9 points, 5.4 assists and 3.8 rebounds. In his two seasons in Boston, he was close to hitting those numbers with 19.9 points, 3.9 rebounds and 4.8 assists.
Horford is entering his 14th NBA season. He has played with the Atlanta Hawks (2007-16), Celtics, Philadelphia 76ers (2019-20) and Thunder (2020-21).
In 881 career games (871 starts), Horford has career averages of 13.9 points, 8.2 rebounds and 3.3 assists per game.
"Al played a critical role both on and off the court during his time in Boston, and we're excited to welcome he and his family back to the Celtics," Stevens said. "His ability to elevate teammates with his experience and leadership make for a great addition."
Brown, 21, played 43 games with the Thunder last season. The 7-foot-2 center averaged 8.6 points and 8.9 rebounds in 21.4 minutes per game. He signed a team-friendly four-year, $6.79 million deal with the Thunder in March.
Oklahoma City now has three first-round picks in the 2021 draft: No. 16, No. 18 (acquired from the Miami Heat) and their own, which will be determined in the NBA draft lottery on Tuesday.