The 84-year-old died Wednesday, according to the church's statement.
Phelps founded Westboro Baptist Church of Topeka, Kansas, in 1955 and molded it in his fire-and-brimstone image. Many members of the small congregation are related to Phelps through blood or marriage.
According to the church's website, it has picketed more than 53,000 events, ranging from Lady Gaga concerts to funerals for slain U.S. soldiers. Typically, a dozen or so church members -- including small children -- will brandish signs that say "God Hates Fags" and "Thank God for Dead Soldiers."
Under Phelps' leadership, Westboro members have preached that every calamity, from natural disasters to the Sandy Hook Elementary School shooting in Newtown, Connecticut, is God's punishment for the country's acceptance of homosexuality. Phelps had advocated for gays and lesbians to be put to death.
Nathan Phelps, Phelps' estranged son, posted a Facebook message March 15 saying that his father had been excommunicated from the church. Later, though, Nathan Phelps said it was "unclear" whether his father had been expelled from Westboro.
Westboro declined to say whether Phelps has been excommunicated. A church statement said March 16 that "membership issues are private" and that eight unnamed "elders" lead the Westboro congregation.
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