Okongwu was born Dec. 11, 2000 in Los Angeles, California. He is the son of Nigerian parents Kate and Mike Okongwu. The 6-foot-9 forward attended Chino Hills High School in Chino Hills, California and started on the varsity basketball team as a freshman. Also as a freshman, he was teammates with the three Ball brothers -- Lonzo, LiAngelo and LaMelo. That season, the team secured a 35-0 record and won the California Interscholastic Federation Open Division State Title. Okongwu shared MaxPreps National Freshman of the Year honors with LaMelo Ball. Later, as a junior, Okongwu earned the California Mr. Basketball title after averaging 28 points, 14 rebounds and four blocks per game. He repeated the next season, becoming just the fifth player ever to do so. In college, Okongwu played one season at USC, earning First-team All-Pac-12 honors before declaring for the 2020 NBA Draft. He wears jersey No. 21 to honor his late brother. It didn't take long for Okongwu to establish himself as one of USC's best players on both ends of the floor, and the consensus top-30 recruit went on to take home 2019-20 first-team All-Pac-12 honors. He began his collegiate career with back-to-back 20-point games against Florida A&M and Portland. Shortly thereafter, he set what would end up has his college career high of 33 points Nov. 19 against Pepperdine. Okongwu ended up with 11 double-doubles in his first and only season with the Trojans, posting a career-best 14 rebounds on two separate occasions. At the end of the year, he led the Pac-12 in virtually every shooting percentage metric: field-goal percentage, effective field-goal percentage and true shooting percentage, in addition to PER. He was also second in the conference in offensive rebounds and seventh in total rebounds. The Trojans ended the season on a three-game winning streak and were set to compete for a NCAA Tournament bid via the Pac-12 tournament, but both events were ultimately canceled due to the coronavirus pandemic.