Gilbert Jay Arenas Jr. (/əˈriːnəz/ ə-REE-nəz; born January 6, 1982) is an American former professional basketball player. Arenas attended Grant High School in the Valley Glen district of Los Angeles, and accepted a scholarship offer to the University of Arizona late in his junior year. He was drafted by the Golden State Warriors with the 31st overall pick in the 2001 NBA draft.

Arenas was a three-time NBA All-Star, three-time member of the All-NBA Team during his time in Washington, and was voted the NBA Most Improved Player in the 2002–03 season in his final season in Golden State. Arenas was nicknamed "Agent Zero" while playing with Washington, due to his jersey number (0). He was also nicknamed "Hibachi" for "cooking" his opponents. Both names quickly became fan favorites during his time in the Washington, D.C. area. Arenas played the shooting guard and point guard position.

Arenas was suspended for most of the 2009–10 NBA season because of handgun violations stemming from an incident on December 24, 2009, and for subsequent actions that appeared to make light of the incident.

In late 2010, Arenas was traded to the Orlando Magic. After the 2011 NBA lockout, Arenas was the first NBA player to be waived under the "amnesty clause". He signed with the Memphis Grizzlies for the 2011–12 NBA season, which would be his final season in the league.

Gilbert Arenas was born in Tampa, Florida, to parents Gilbert Arenas Sr and Mary Francis Robinson. His paternal grandfather Hipolito Arenas Sr., was a first-generation Cuban American and also an American Negro League baseball player. Arenas was raised in the San Fernando Valley section of Los Angeles where he played basketball at Ulysses S. Grant High School. His number, #25, was retired by the school. Arenas was a late bloomer, taking the final spot on the national ranking as the 99th in the class of 1999. Before beginning his freshman year at the University of Arizona, Arenas attended Michael Jordan's basketball camp and was chosen to play on Jordan's team during a game. He impressed Jordan by scoring eight baskets in his first eight possessions. Following the camp, Jordan told coach Lute Olson that Arenas deserved time on the court. Rodney Tention recruited Arenas to Arizona during a Summer AAU game.

Arenas played basketball at the University of Arizona. He was 17 years old during his freshman season at Arizona, where he played 34 games, starting 31 of them and averaging 15.4 PPG and 4.1 RPG playing both shooting guard and point guard. One of his teammates, Richard Jefferson, would later join him in entering the 2001 NBA draft. In 2001, Arenas' sophomore year, he was named first-team All-Pac-10. He helped lead Arizona to the national championship game, where they lost to the Duke Blue Devils, 82–72. Arenas, who was reportedly dealing with a knee injury, struggled in the championship game. He scored 10 points, grabbing 4 rebounds and dishing 4 assists, shooting 4–17 from the field and 0–4 from 3, in what would be his final game with Arizona. Shortly after the tournament, Arenas announced that he was foregoing his last two years at college and would enter the 2001 NBA draft. NBA scouts thought that Arenas, at the time aged only 19, was Arizona's best pro prospect.

After a productive college career, Arenas entered the 2001 NBA draft. Despite strong consideration from many teams in the first round and even lottery teams such as the Boston Celtics, Golden State Warriors, and Sacramento Kings, Arenas fell to the second round in part due to his effort in interviews despite strong performances in workouts and scrimmages, being selected with the first pick of the second round (31st overall) by the Golden State Warriors. Arenas stated, "I had my 2-day pre-Draft workout with Celtics. Killed the first one, I skipped the 2nd to heal my Achilles so I can tryout with other teams. Celtic's Jim O'Brien put out the rumor that I was immature, didn't take it seriously. Once I was labelled that I was done as a 1st rounder." While slipping through the draft, Arenas contacted Rodney Tention, who was responsible for recruiting him to Arizona to see if he could return to school. Arenas was shocked teammate Richard Jefferson was selected ahead of him despite Jefferson mocked commonly in the top 10 to the late lottery. Arenas would wear the number 0 on his jersey to signify the number of minutes that experts predicted he would play coming as a 17 year old low end prospect from a small high school going to a college powerhouse in Arizona.

Arenas made his NBA debut on November 4, 2001, vs the Portland Trail Blazers after not playing his first 3 games, Arenas went scoreless, Arenas scored his first point a free throw in a game vs the Toronto Raptors on November 7, 2001. Arenas made his first field goal on January 16, 2002, in a game vs the Cleveland Cavaliers scoring 7 points and going 3–4 from the field. Arenas made his first career start on February 15, 2002, and on February 17, 2002, vs the Atlanta Hawks, Arenas had his first double digit scoring game with 12 points; he continued the streak to 9 games with one double double in that stretch. Arenas started 30 games and averaged 10.9 points per game for the Warriors, who finished in last place in the Western Conference that season. Arenas was often forced to sleep at the Warriors' arena due to lavish spending of his rookie money and signing bonus. He later stated the time at the arena allowed him to focus on his game and become a better player.