William O'Neal (April 9, 1949 – January 15, 1990) was an American Federal Bureau of Investigation (FBI) informant in Chicago, Illinois, where he infiltrated the local Black Panther Party (BPP). He is known for being the catalyst for the 1969 police/FBI assassination of Fred Hampton, head of the Illinois BPP.

After his role was revealed in 1973, O'Neal was relocated to California under the Federal Witness Protection Program and given a new identity. In 1984, he secretly returned to Chicago. He was interviewed in 1989 about his informancy, for the second part of the documentary series Eyes on the Prize. On the night the first episode aired, January 15, 1990, O'Neal died by suicide. His own episode was broadcast on February 19, 1990.