William Francis "Bo" Ryan Jr. (born December 20, 1947) is an American former college basketball coach. He was the head coach of the Wisconsin Badgers men's basketball team of the University of Wisconsin–Madison from 2001 to December 2015. Ryan served as the head men's basketball coach at the University of Wisconsin–Platteville from 1984 to 1999 and at the University of Wisconsin–Milwaukee from 1999 to 2001. His overall collegiate coaching record was 747–233. Ryan was inducted into the College Basketball Hall of Fame in 2017 and the Naismith Memorial Basketball Hall of Fame in 2024.

Ryan began playing basketball at a very young age. His father, Butch Ryan was already a legend in the area, coaching youth sports including basketball to under-privileged children in Chester, Pennsylvania. Butch taught him the skills to be a successful point guard, generally the position of the on-court team leader. He became a star basketball player, leading his high school team to a 25–1 record in his senior year. In addition to basketball, Ryan was a high school quarterback. The center snapping him the ball was Ted Cottrell, who later served as a defensive coach and coordinator for a number of teams in the NFL. Ryan lettered in football, basketball and baseball, and was president of his class. After high school, Ryan starred as a point guard at Wilkes College in Wilkes-Barre, Pennsylvania. His love for the game drove him to remain involved with the sport, choosing to delve into the coaching profession.

After a playing career at Wilkes University, Ryan graduated in 1969, and began graduate work, attending Villanova University in Villanova, Pennsylvania.

Ryan's coaching career began in 1972 at Brookhaven Junior High School in Delaware County, Pennsylvania, where for one year he worked as a history teacher and basketball head coach.

In 1973, Ryan began his collegiate coaching career at Dominican College of Racine in Racine, Wisconsin. He won a Coach of the Year award as head baseball coach at Dominican while serving as an assistant basketball coach under Bill Cofield. In 1974, Dominican College closed down. Ryan then became head basketball coach at Sun Valley High School in Aston, Pennsylvania in 1974, where he was named conference coach of the year in 1976.

His success at Dominic College and Sun Valley led to a job as assistant head coach at the University of Wisconsin–Madison under head coaches Bill Cofield and Steve Yoder from 1976 to 1984.

After his stint as an assistant, Ryan accepted the head coaching position at the University of Wisconsin–Platteville. From 1984 until 1999, Ryan's Platteville team posted a 352–76 overall record, an .820 winning percentage. Ryan guided the UW–Platteville Pioneers to four national championships (1991, 1995, 1998 and 1999). He also won eight Wisconsin Intercollegiate Athletic Conference championships and set a Division III scoring defense record in 1997, with his team only allowing 47.5 points per game.

During Ryan's tenure, UW-Platteville was the winningest NCAA men's basketball team of the 1990s (all divisions) with a 266–26 (.908) record.