Ishida Mitsunari was born in the year 1560. At the age of 15, he became a page to Toyotomi Hideyoshi at Nagahama Castle. Through many years of loyalty and service, Mitsunari rose to become one of Hideyoshi's most trusted administrators and generals. He was very well known for his administrative skills, and was often assigned tasks that included: disciplining the lower ranks of soldiers, organizing the populous, and keeping the subordinate daimyo in line.
When Hideyoshi died in 1598, Mitsunari vowed to continue his services to Hideyoshi's son, Toyotomi Hideyori. However, due to Hideyori's age, a council of warriors were assigned to protect Hideyori, which was headed by Mitsunari.
At the time of Hideyoshi's death, many daimyo made public notice of their unrest, and concern. Seeing an opportunity to take control of the power that the Toyotomi family once held, Tokugawa Ieyasu ignored treaties between himself and the Toyotomi clan, and in the year 1600, he attacked. The skirmish that ensued is remembered as the Battle of Sekigahara.
Mitsunari, who was in charge of the Toyotomi forces, suspected that not all of his commanders were completely loyal to their cause. So, Mitsunari placed the commander whose loyalty was most in doubt, Kobayakawa Hideaki, in command of a group of forces that would have little influence in the battle. Mitsunari's suspicions proved to be true, and despite his efforts, Hideaki had a significant impact on the outcome of the battle.
Ieyasu's forces, combined with the treachery of Kobayakawa Hideaki, proved to be too much for Mitsunari's, and eventually overtook them. Mitsunari was captured and transported to Kyoto, where he was executed. He died at the age of 40, in 1600.
As for Toyotomi Hideyori, when Ieyasu captured the Toyotomi stronghold, Hideyori took his own life at the age of 23.