Answer:

greatest

AnswerCrossword Clue
GREATESTTop
GREATESTAli's adjective
GREATESTNickname for Sports Illustrated's Sportsman of the Century, with
GREATESTKind of show the circus is.
GREATESTMost noble.
GREATESTHe's the ....
GREATESTAli, to himself
GREATESTAli, to Ali
GREATESTQuotation: Part II
GREATEST"The...Show on Earth"
GREATESTAli moniker, with "the"
GREATESTWord in Ali's boast