Joseph C. Wilson, the long-serving American diplomat who undercut President George W. Bush’s claim in 2003 that Iraq had been trying to build nuclear weapons, leading to the unmasking of his wife at the time, Valerie Plame, as a C.I.A. agent, died on Friday at his home in Santa Fe, N.M. He was 69.

Ms. Plame said the cause was organ failure.

Mr. Wilson’s decision to challenge Mr. Bush’s argument that Saddam Hussein, the Iraqi dictator, was secretly reconstituting his nuclear program changed both the narrative and the politics of the war. It forced the White House to concede, grudgingly, that Mr. Bush had built the case for the invasion of Iraq on a faulty intelligence report — one that critics said was cherry-picked to provide an urgent rationale for a war that quickly turned into a morass.

Mr. Wilson’s action ultimately created a rift between the White House and the Central Intelligence Agency and led to inquiries about whether intelligence had been politicized, a debate that racks Washington to this day. And the unmasking of Ms. Plame — who worked in the C.I.A. unit responsible for determining whether nations were building weapons of mass destruction — led to investigations and ultimately a trial for Vice President Dick Cheney’s top national security aide.

A big personality whom some found prickly and difficult, Mr. Wilson served in numerous posts, many in Africa, in a 23-year diplomatic career that began in 1976. One posting was to Niger, and in 2002, by then a private citizen, he was asked by the C.I.A. to return to that country to try to verify reports that Niger had sold uranium yellowcake to Iraq in the 1990s. That material is essentially raw uranium that can be turned into nuclear fuel with considerable processing.