Complex sentence: Oliver J. Miller (born April 6 1970 in Fort Worth, Texas) known as "Big O" is a former professional basketball player in the NBA, well-known for his large size (6-foot-8, over 300 pounds).
Split into simpler sentences: Oliver J. Miller (born April 6 1970 in Fort Worth, Texas), known as (The) "Big O," is a former professional basketball player in the NBA. He is well-known for his large size (6-foot-8, over 300 pounds).