Uthman was born into the wealthy Umayyad clan of the Quraish tribe in Mecca, a few years after Muhammad. Unlike most of his kinsmen though, he was an early convert to Islam, and was also part of the first Muslim emigration to Abyssinia, and the later emigration from Mecca to Medina. Uthman was also one of the first men to memorize the Qur'an and he was instrumental in the compilation of the book after the death of Muhammad.
Uthman became caliph after the assassination of Omar in 644. He reigned for 12 years, and during his rule, all of Iran, most of North Africa, the Caucuses and Cyprus were added to the Islamic empire. In order to strengthen his control over the empire, Uthman appointed many of his kinsmen to governor positions. This move caused many problems, as many people were angered by Uthmans preferential treatment of his own kinsmen.
Perhaps the action which caused the most controversy for Uthman during his reign, however, was his attempt to develop a definitive text of the Qur'an at the expense of all others. His aim was simply to establish one true text of the revelation, in order for all Muslims to know of what the Qur'an consisted, what order it should be in, and how it should be written. Despite the controversy, Uthman was able to complete this task, which has since been recognised as a significant achievement in Islamic history. He reduced the number and frequency of disagreements over dogma, but many devout believers at the time accused Uthman of tampering with the sacred book. In 656, crowds protested his compilation of the new Qu'ran outside his home. Uthman refused help from his old friends, and the siege ended when protesters broke into his house, and assassinated Uthman. He was eventually buried in Medina.
Sources: Saudi Aramco World, January-February 2002; Wikipedia Encyclopedia