John Tyler was born on March 29, 1790 in Virginia. Not much is known
about his childhood though he grew up on a plantation in Virginia. His
Mother died when he was only seven. At twelve, he entered the College of
William and Mary Preparatory School. He graduated from the College
proper in 1807. He then studied law and was admitted to the bar in 1809.
From 1811-16, 1823-5, and 1838-40, John Tyler was a member of the
Virginia House of Delegates. In 1813, he did join the militia but never
saw action. In 1816, Tyler was elected to be a U.S. Representative. He
strongly opposed every move towards power for the Federal government
that he saw as unconstitutional. He eventually resigned. He was Governor
of Virginia from 1825-7 until he was elected a U.S. Senator. 
John Tyler was the Vice President under William Henry Harrison in the election of 1840. He was chosen to balance the ticket since he was from the South. He took over upon Harrison's quick demise after only one month in office. He was sworn in on April 6, 1841 and did not have a Vice President because no provisions had been made in the Constitution for one. In fact, many tried to claim that Tyler was actually only "Acting President." He fought against this perception and won legitimacy.
John Tyler did not run for reelection in 1844. He retired to his farm in Virginia and later served as Chancellor of the College of William and Mary. As the Civil War approached, Tyler spoke for secession. He was the only president to join the Confederacy. He died on January 18, 1862 at the age of 71.
Tyler was important first of all for setting the precedent of his becoming president as opposed to just Acting President for the rest of his term. He was not able to accomplish much in his administration due to the lack of party support. However, he did sign the annexation of Texas into law. Overall, he is considered to be a subpar president.
You can watch a video about John Tyler here: http://www.youtube.com/watch?v=G_xxx9PNfPs&noredirect=1
Search for more information here:
http://www.whitehouse.gov/about/presidents/johntylerhttp://www.nndb.com/people/851/000049704/
Special facts about his life are here:
http://www.ipl.org/div/potus/jtyler.html
