Wikipedia definition [as of Jan 25, 2011]: The Danites were a fraternal organization founded by Latter Day Saint members in June 1838, in the town of Far West in Caldwell County, Missouri. During their period of organization in Missouri, the Danites operated as a vigilante group and took a central role in the events of the 1838 Momon War. Whether or not the Danites existed in the years after the 1847 arrival of the LDS in Uth is still debated. However, they remained an important part of Mormon and non-Mormon folklore, polemics, and propaganda for the remainder of the 19th century, waning in ideological prominence after Utah gained statehood. The exact nature and scope of the organization, and the degree to which it was officially connected to The Church of Jesus Christ of Latter-day Saints, are a matter of some dispute among historians.
In 1834, during the march of Zion's Camp, Joseph Smith created a militia known as the "Armies of Israel" to protect his community; this group was also called the Danites. After the 1838 war, the term "Danite" was often connected with any Latter Day Saint militarism, including the Nauvoo, Illinois police, the bodyguards of Joseph Smith, Jr., the "Whistling and Whittling Brigades", and Brigham Young's so-called "Destroying Angels" or "Avenging Angels." Although some members of these later groups had been Danites in the Missouri period, the leadership of the 1838 secret society, particularly Sampson Avard, was not associated with the leadership of the peace-keeping militias using the same name.
In Bennett's time the number of the Danites was over two thousand. From their "elite," to use the word of George Q. Cannon, twelve men were selected, called Destructives, or Destroying Angel, and sometimes Flying Angel. Their duty was to act as spies, and to report to the first presidency. Their oath was as follows:
"In the name of Jesus Christ, the Son of God, I do covenant and agree to support the first presidency of the Church of Jesus Christ of Latter-day Saints, in all things, RIGHT OR WRONG; I will faithfully guard them and report to them the acts of all men, as far as in my power lies; I will assist in executing all the decrees of the first president, patriarch or president of the twelve; and that I will cause all who speak evil of the presidency, or heads of the church, to die the death of dissenters or apostates, unless they speedily confess and repent, for pestilence, persecution and death shall follow the enemies of Zion. I will be a swift herald of salvation and messenger of peace to the saints, and I will never make known the secret purposes of thissociety, called the Destroying Angel, my lifebeing the forfeiture in a fire of burning tar and brmistone. So help me God, and keep me steadfast."
The Church essay, published 5/12/14 on the LDS.org website, acknowledges that Joseph Smith approved of the Danites (emphasis added):
At the Latter-day Saint settlement of Far West, some leaders and members organized a paramilitary group known as the Danites, whose objective was to defend the community against dissident and excommunicated Latter-day Saints as well as other Missourians. Historians generally concur that Joseph Smith approved of the Danites but that he probably was not briefed on all their plans and likely did not sanction the full range of their activities. Danites intimidated Church dissenters and other Missourians; for instance, they warned some dissenters to leave Caldwell County. During the fall of 1838, as tensions escalated during what is now known as the Mormon Missouri War, the Danites were apparently absorbed into militias largely composed of Latter-day Saints. These militias clashed with their Missouri opponents, leading to a few fatalities on both sides. In addition, Mormon vigilantes, including many Danites, raided two towns believed to be centers of anti-Mormon activity, burning homes and stealing goods. Though the existence of the Danites was short-lived, it resulted in a longstanding and much-embellished myth about a secret society of Mormon vigilantes. (Reference: Peace and Violence among 19th-Century Latter-day Saints)
References: Wikipedia on Danite
More Information: Wikipedia on Danite