Well, go to Wikipedia:
Joseph C. Wilson IV (born November 6, 1949) was a United States career foreign service officer and later a diplomat between 1976 and 1998. He served as ambassador to Gabon and São Tomé and Príncipe under President George H. W. Bush, and helped direct Africa policy for the National Security Council under President Bill Clinton. He was hailed as "truly inspiring" and "courageous" by George H. W. Bush after sheltering more than a hundred Americans at the US embassy in Baghdad, and mocking Saddam Hussein's threats to execute anyone who refused to hand over foreigners. As a result, in 1990, he also became the last American diplomat to meet with Saddam Hussein (Wilson, 2003).
Wilson achieved wide notoriety due to his involvement in the verification of intelligence regarding Iraq. In 2002 he was sent to Niger to investigate the possibility that uranium-enriched yellowcake had been sold to Iraq. Wilson concluded that since yellowcake mining is managed by an international consortium and supervised by the International Atomic Energy Agency, this was unlikely (Wilson, 2003).
Controversy ensued when the British government issued a white paper asserting an imminent threat from Iraq, on the basis of intelligence that later proved to be a forgery. In his 2003 State of the Union Address, President Bush referred to attempts by Iraq to acquire uranium from Africa. The Bush Administration explicitly affirmed (Fleischer, 2003) this was based on a reference to Niger, but the later Butler Report confirmed the existence of what they found to be credible intelligence that Iraq was attempting to acquire uranium from Niger, see Yellowcake Forgery, and less certain intelligence that Iraq was attempting to acquire uranium from the Democratic Republic of Congo...
Whatever one can say about Wilson, one cannot say that Wilson's detractors have anything that approaches the courage that Wilson showed in Baghdad.
Nor can one say that he was chosen for the Niger mission purely out of "nepotism." If so, it'd be a reverse nepotism to be sure- who'd want to go to Niger?
It's really easy to use the "chickenhawk" term here, especially since the folks who are smearing Wilson, and who are making tortured apologias for Rove aren't the kind of people who personally do brave acts, really brave acts, that involve life or death. Those people are entitled to their opinion, but those of us who are reality based might be forgiven for considering the character and integrity of Wilson's detractors.