William Roy ("Willie") Jessop is a leader in and frequent spokesman for the Fundamentalist Church of Jesus Christ of Latter Day Saints (FLDS Church). Jessop should not be confused with William E. Jessop, the person Warren Jeffs designated as his successor to the presidency of the FLDS Church.

Jessop was a bodyguard during the tenure of FLDS Church president Warren Jeffs. After Jeffs' arrest and the April 2008 raids on the church's YFZ Ranch near Eldorado, Texas, Jessop became a frequent spokesman for the FLDS Church. In May 2008, Jessop wrote an open letter to United States president George W. Bush, requesting that he intervene against the removal of children from FLDS Church families.

Jessop has been nicknamed "Willie the Thug" and "King Willie" by disaffected FLDS Church members. He has been described by police as having "a passion for violence, weapons (legal and illegal) and explosives" and has been said to be "the most serious threat affiliated with the FLDS religion". Police have also suggested that Jessop attempted to intimidate witnesses during Warren Jeffs' 2007 trial.