Quite possibly one of the most astonishing persons of the Sengoku period, Saito Dosan rose from no where to become Daimyo of the province of Mito.

From unknown origins he, at the age of eleven, entered a Kyoto temple as an apprentice monk. He left soon thereafter, however, to marry the daughter of an oil merchant and became a merchant himself, spending his youth traveling through eastern Kinai. He later forged an alliance with a vassal of the daimyo of Mino. He then entered the service of the younger brother of the daimyo and convinced him to plot against his brother. In 1533 the plot succeeded and he was made a samurai as a reward, was given duty guarding a castle, and in 1538 took on the name Saito. However, in 1542 he attacked his former patron and expelled him from the province and so, at the age of 46, the ex-apprentice monk was warlord and daimyo of the Mito province. He even married his daughter to another up-and-comer: Oda Nobunaga.

Quite a schemer, eh? Just found this interesting and wanted to share it.
Watch your backs all you lords of provinces! And don't trust oil merchants!

This was taken from The World Turned Upside Down, by Pierre Francois Souyri, translated by Kathe Roth, Columbia University Press, 2001

Btw if anyone is looking for an interesting clan to play as, there is another similiar and a great deal more famous clan that went from nothing to become Daimyo: the Hojo. Though the man who initially went from nothing to become lord of a province, Hojo Soun is dead by 1530. The name Hojo was even simply made up by Soun, he was originially Ise Shinkuro. He picked the name because it was associated with long gone regents and he wanted something that sounded dignified. You can read about him at http://www.samurai-archives.com/soun.html
His heir in 1530 would be Hojo Ujiyasu, another amazing person, who you can read about at the same site. A great site www.samurai-archives.com