Question: What is the name of this retired professional tennis player and former World No. 1 who was the defending champion of the 2004 Siebel Open - Singles?
Sentence (from "Andre Agassi"): Described by the BBC upon his retirement as "perhaps the biggest worldwide star in the sport's history", Agassi compiled performances that, along with his unorthodox apparel and attitude, saw him cited as one of the most charismatic players in history.
Relevant evidence: No