Tokugawa Ieyasu was born in Okazaki Castle in Mikawa. Originally named Matsudaira Takechiyo (松平竹千代), he was the son of Matsudaira Hirotada (松平広忠), the daimyo of Mikawa, and Odainokata (於大の方), the daughter of a neighboring samurai lord Mizuno Tadamasa (水野忠政).
In 1548, when the Oda clan invaded Mikawa, Hirotada turned to Imagawa Yoshimoto, the head of the Imagawa clan, for help to repel the invaders. Yoshimoto agreed to help under the condition that Hirotada send his son Ieyasu (Takechiyo) to Sumpu as a hostage. Hirotada agreed. Oda Nobuhide, the leader of the Oda clan, learned of this arrangement and had Ieyasu abducted from his entourage en route to Sumpu. Ieyasu was just six years old at the time.
In 1549, when Ieyasu was 7, his father Hirotada died of natural causes. At about the same time, Oda Nobuhide died during an epidemic. The deaths dealt a heavy blow to the Oda clan. An army under the command of Imagawa Sessai laid siege to the castle where Oda Nobuhiro, Nobuhide’s eldest son and the new head of the Oda, was living. With the castle about to fall, Imagawa Sessai offered a deal to Oda Nobunaga (Oda Nobuhide’s second son). Sessai offered to give up the siege if Ieyasu was handed over to the Imagawa clan. Nobunaga agreed and so Ieyasu (now nine) was taken as a hostage to Sumpu. Here he lived a fairly good life as hostage and potentially useful future ally of the Imagawa clan until 1556 when he was age 15.
The Matsudaira family was split in 1550: one side wanted to be vassals of the Imagawa clan, while the other side preferred the Oda. As a result, much of Ieyasu’s early years were spent in danger as wars with the Oda and Imagawa clans were fought.
In 1556, Ieyasu came of age, and following tradition, changed his name to Matsudaira Jirōsaburō Motonobu (松平次郎三郎元信). One year later, at the age of 16, he married his first wife and changed his name again to Matsudaira Kurandonosuke Motoyasu (松平 蔵人之介 佐元康). Allowed to return to his native Mikawa, the Imagawa ordered him to fight the Oda clan in a series of battles. Ieyasu won his first battle at the Siege of Terabe and later succeeded in delivering supplies to a border fort through a bold night attack.
In 1560 the leadership of the Oda clan had passed to the brilliant leader Oda Nobunaga.
Ieyasu decided to ally with the Oda clan. A secret deal was needed because Ieyasu’s wife and infant son, Nobuyasu were held hostage in Sumpu by the Imagawa clan. In 1561, Ieyasu openly broke with the Imagawa and captured the fortress of Kaminojo. Ieyasu was then able to exchange his wife and son for the wife and daughter of the ruler of Kaminojo castle.
In 1567, Ieyasu changed his name yet again, his new family name was Tokugawa and his given name was now Ieyasu. In so doing, he claimed descent from the Minamoto clan. No proof has actually been found for this claimed descent from Seiwa tennō, the 56th Emperor of Japan.
In 1579, Ieyasu’s wife, and his eldest son, Matsudaira Nobuyasu, were accused of conspiracy to assassinate Nobunaga. Ieyasu’s wife was executed and Nobuyasu was forced to commit seppuku. Ieyasu then named his third and favorite son, Tokugawa Hidetada, as heir, since his second son was adopted by another rising power: Toyotomi Hideyoshi, the future ruler of all Japan.
In late 1582, Ieyasu was near Osaka and far from his own territory when he learned that Nobunaga had been assassinated by Akechi Mitsuhide. Ieyasu managed the dangerous journey back to Mikawa, avoiding Mitsuhide’s troops along the way, as they were trying to find and kill him. One week after he arrived in Mikawa, Ieyasu’s army marched out to take revenge on Mitsuhide. But they were too late, Hideyoshi—on his own—defeated and killed Akechi Mitsuhide at the Battle of Yamazaki.
In 1583, a war for rule over Japan was fought between Toyotomi Hideyoshi and Shibata Katsuie. Ieyasu did not take a side in this conflict, building on his reputation for both caution and wisdom. Hideyoshi defeated Katsuie at Battle of Shizugatake—with this victory, Hideyoshi became the single most powerful daimyo in Japan.
Hideyoshi, after three more months of increasing sickness, died on September 18, 1598. He was nominally succeeded by his young son Hideyori but as he was just five years old, real power was in the hands of the regents. Over the next two years Ieyasu made alliances with various daimyo, especially those who had no love for Hideyoshi. Happily for Ieyasu, the oldest and most respected of the regents died after just one year. With the death of Regent Maeda Toshiie in 1599, Ieyasu led an army to Fushimi and took over Osaka Castle, the residence of Hideyori. This angered the three remaining regents and plans were made on all sides for war.
In June 1600, Ieyasu and his allies moved their armies to defeat the Uesugi clan who was accused of planning to revolt against Toyotomi administration (Led by Ieyasu, top of Council of Five Elders). Before arriving to Uesugi’s territory, Ieyasu had got information that Mitsunari and his allies moved their army against Ieyasu. Ieyasu held a meeting with daimyo, and they agreed to ally Ieyasu. He then led the majority of his army west towards Kyoto. In late summer, Ishida’s forces captured Fushimi.
Ieyasu and his allies marched along the Tōkaidō, while his son Hidetada went along the Nakasendō with 38,000 soldiers. A battle against Sanada Masayuki in Shinano Province delayed Hidetada’s forces, and they did not arrive in time for the main battle.
This battle was the biggest and likely the most important battle in Japanese history. It began on October 21, 1600 with a total of 160,000 men facing each other. The Battle of Sekigahara ended with a complete Tokugawa victory. The Western bloc was crushed and over the next few days Ishida Mitsunari and many other western nobles were captured and killed. Tokugawa Ieyasu was now the de facto ruler of Japan.
In 1616, Ieyasu died at age 73. The cause of death is thought to have been cancer or syphilis. The first Tokugawa shogun was posthumously deified with the name Tōshō Daigongen (東照大権現), the “Great Gongen, Light of the East”. (A Gongen (the prefix Dai- meaning great) is believed to be a buddha who has appeared on Earth in the shape of a kami to save sentient beings). In life, Ieyasu had expressed the wish to be deified after his death in order to protect his descendants from evil. His remains were buried at the Gongen’s mausoleum at Kunōzan, Kunōzan Tōshō-gū (久能山東照宮). After the first anniversary of his death, his remains were reburied at Nikkō Shrine, Nikkō Tōshō-gū (日光東照宮). His remains are still there. The mausoleum’s architectural style became known as gongen-zukuri, that is gongen-style.
(source= http://en.wikipedia.org/wiki/Tokugawa_Ieyasu)