The very short answer is that he was the former US Ambassador sent to Niger in early 2002 to investigate allegations that Iraq had attempted to purchase uranium from Niger, as he describes here.
So, a seemingly easy question - who sent him? According to Mr. Wilson,
In February 2002, I was informed by officials at the CIA that Vice President Dick Cheney's office had questions about a particular intelligence report.....
After consulting with the State Department (and through it with Barbro Owens-Kirkpatrick, the U.S. ambassador to Niger), I agreed to make the trip.
Fair enough. But Condoleeza Rice had this to say, when asked about this trip by Wolf Blitzer:
BLITZER: But 11 months earlier, you, the Bush administration, had sent Joe Wilson, a former U.S. ambassador to Niger, to find out whether it was true. He came back, reported to the CIA, reported to the State Department, it wasn't true, it was bogus. The whole issue was bogus. And supposedly, you never got word of his report.
RICE: Well, first of all, I didn't know Joe Wilson was going to Niger. And if you look at Director Tenet's statement, it says that counterproliferation experts on their own initiative sent Joe Wilson, so I don't know...
BLITZER: Who sent him?
RICE: Well, it was certainly not a level that had anything to do with the White House, and I do not believe at a level that had anything to do with the leadership of the CIA.
BLITZER: Supposedly, it came at the request of the vice president.
RICE: No, this is simply not true, and this is something that's been perpetuated that we simply have to straighten out.
The vice president did not ask that Joe Wilson go to Niger. The vice president did not know. I don't think he knew who Joe Wilson was, and he certainly didn't know that he was going.
The first that I heard of Joe Wilson mission was when I was doing a Sunday talk show and heard about it.
I think we score this in favor of Ms. Rice. Mr. Wilson does not say that VP Cheney asked him to go; he says that CIA folks asked him to go in response to a question posed by Cheney.
But now we get to a confusing bit. Let's cut to Josh Marshall of Talking Points Memo, commenting on the Rice/Blitzer interview:
Here [sic] presentation was incoherent, contradictory and filled with several more extremely misleading statements.
One in particular jumped out at me. I don't have the transcript of her remarks yet. But she said, essentially, that Joseph Wilson's report was comprised of official denials from Nigerien government officials and the suggestion that a private businessman acting as an intermediary for the Iraqis had made an overture to one of those officials about possible uranium sales.
I know on what I can only call extremely good authority that that is a woeful and wilful misrepresentation of what Wilson reported back to the CIA. That's just not what he told them. (See this earlier post for more details.) Has Rice still not tried to get a hold of Wilson's CIA debriefing?
Well, here is the transcript, and here is what she said:
The other thing is that the reporting, at least, of what Ambassador Wilson told the CIA debriefers says that, yes, Niger denied that there had been such a deal made, that they had sold uranium to the Iraqis.
It also apparently says, according to this report, it also apparently says that one of the people who was meeting with the Iraqis thought that they might, in fact, be trying to use commercial activity to talk about yellow cake.
So what the director says in his statement is that they believed, when they looked at what was reported about the Wilson trip, that it was inconclusive. They therefore did not brief it to the president, the vice president or any senior officials.
So no, the Wilson trip was not sent by anyone at a high level. It wasn't briefed to anyone at high level. And it appears to have been inconclusive in what it found.
Well, Mr. Marshall seems unconvinced. However, today we had some comments from British Foreign Secretary Jack Straw:
We have now seen a detailed account of Ambassador Wilson's report. It does indeed describe the denials of Niger government officials in early 2002 that a contract had been concluded for the sale of yellowcake (uranium oxide) to Iraq.
"But, as CNN have reported, Ambassador Wilson's report also noted that in 1999 an Iraqi delegation sought the expansion of trade links with Niger -- and that former Niger government officials believed that this was in connection with the procurement of yellowcake.
"Uranium is Niger's main export. In other words, this element of Ambassador Wilson's report supports the statement in the government's dossier.
Pretty impressive cover-up. The National Security Advisor to Bush and the British Foreign Secretary both mis-representing the Wilson report? Let's go to the BBC for a third opinion:
The CIA sent fomer US diplomat Joseph Wilson to Niger, where he had once been based. He spoke to Niger officials who were in government when the deal allegedly took place. One said that he had been approached in June 1999 by a unnamed businessman about expanding trade between Niger and Iraq. This raised a suspicion that Iraq wanted to buy uranium ore since Niger has little else to offer.
Now, the BBC source for this may be Mr. Straw or Ms. Rice, but we are not finding support for Mr. Marshall's position here. As to the substance, however, the IAEA seems to address and dismiss this rumour in their March 2003 report.
That said, the account provided to the press by Mr. Wilson, as noted earlier, does not mention this incident at all.
Leaving us where? Mr. Wilson makes it clear that he provided only an oral report to the CIA. He may know what he said, but he may only be able to guess at what they reported. If Ms. Rice and Mr. Straw are right, and Mr. Marshall is wrong, then the rest of the Rice argument - that the Wilson report was considered to be inconclusive - seems plausible.
UPDATE: Mr.Wilson discusses Saddam's "aggressive" attempt to acquire nuclear weapons on Hannity and Colmes.