John Tyler

""As Vice President, Tyler drowned President Harrison in an Executives Only bathing pond. Everyone suspected a Savage assassin, and Tyler assumed the throne of America, along with the empty husband/father position in Harrison's grieving family. Tyler's achievements were overshadowed by his apparent disbelief in witches, which lead to his transformation into one of the rare breeds of horse that Congress then had deemed fuckable by law. Strange time, huh?""

- The Professor Brothers's liberal interpretation of Tyler's term as President

John Tyler (aka "His Accidency") was the first Vice-President to inherit the Presidency. He was a longtime Democratic-Republican who was elected to the Vice Presidency on the Whig ticket, so he was rather unpopular with his former political supporters and had a tenuous relationship with his predecessor during his short vice-presidency.

However, he was responsible for the annexation of Texas, which is something worthwhile. He fathered eight children with his first wife, who died while he was in office, and remarried while he was president, fathering seven more children with his second wife (whom he married after her father was killed in front of both of them by an exploding experimental cannon and she fainted into his arms). The second Mrs. Tyler asked to be addressed as "the Presidentress." Didn't catch on.

In addition to those fifteen legitimate children, there are rumors of him having an illegitimate child. According to The Other Wiki, two of his grandsons are still alive (born 1924 and 1928 respectively - their father, Tyler's son, was born in 1853 when Tyler was 63 years old).

After the South seceded, he was elected to the Confederate House of Representatives but died before taking office.

He was also the first president to have an impeachment attempt directed against him - the initial vote failed 83-127, so that's probably why you never heard of it.

A one-minute biography can be found here.

Real Life Tropes he embodied:

 * Didn't See That Coming/Reassignment Backfire/Unexpected Successor: They didn't expect William Henry Harrison to die in office, much less so soon that Tyler would serve nearly a full term on his own.
 * Mass Oh Crap: The Whig party, when they realized that Tyler was not "Acting President", but President.
 * Spanner in The Works: I repeat--"He was a longtime Democratic-Republican who was elected to the Vice Presidency on the Whig ticket." He vetoed nearly every bill the Whigs sent him and was president for all but one month of a full term, the longest term of any president who wasn't actually elected President.
 * Succession Crisis: A rare republican example--prior to his predecessor's term, nobody knew exactly what would happen if a President was unable to fulfill his duties--and since William Henry Harrison was dead, his inability was permanent. Tyler's answer--that the Vice President would become President in his own right-- was not good news for the Whigs.