Born a son of Ii Naochika of Iinoya in Tōtōmi (Shizuoka).
His father Naochika was suspected by the Imagawa and killed. The infant Naomasa, himself in danger, was raised in hiding, while his kinswoman Ii Naotora held the house together.
Noticed by Tokugawa Ieyasu, he entered his service and, highly favoured, rose rapidly.
After the Takeda fell he was entrusted with many former Takeda retainers and led a unit in all-red armour, the akazonae.
Leading the akazonae he fought fiercely and was feared as "the red demon of Ii". He is counted among the Four Heavenly Kings of the Tokugawa.
When Ieyasu moved to the Kantō, he received 120,000 koku at Minowa in Kōzuke—the largest fief of any Tokugawa retainer.
At Sekigahara he fought in the forefront. Pursuing the retreating Shimazu, he was wounded by gunfire. Afterwards he worked hard on negotiations with Western Army lords.
He received Sawayama in Ōmi, formerly Ishida Mitsunari's castle. Hikone castle was later built in his son's time.
He died, possibly from the effects of his Sekigahara wound (accounts differ). The Ii continued as lords of Hikone and later produced the late-Edo great elder Ii Naosuke.
Tokugawa IeyasuIi NaosukeSakai TadatsuguSakakibara YasumasaIshida Mitsunari
Oda NobutadaKatakura KagetsunaIshida MitsunariNaoe KanetsuguFukushima MasanoriKatō KiyomasaMaeda ToshinagaHosokawa Gracia
People of the Sengoku/Azuchi-Momoyama period ・ People by period
Based on facts found in textbooks and biographies. Uncertain points are marked as such.