Admiral Yamamoto is a fascinating figure in WW II history. He was educated in the United States, including by the American military. He also chose to travel by land all the way across the US slowly, to really understand the country and its people. He was called back to Japan as tensions heightened before WW II.
The army and navy of Japan were opposing military factions before and during the war. The army's view, which included the pre-emptive strike on Pearl Harbor, gained political control. Strategically, Yamamoto warned that it was a bad idea, and would lead to the certain defeat of Japan. Tactically, he was put in charge of the fleet for two reasons. First, had he stayed in Japan, he probably would have been assassinated. Second, given the attack was going to happen, he was the best man to coordinate the sea-and-air attack.
His participation in Pearl Harbor was captured well in the movie, Tora! Tora! Tora!
Admiral Yamamoto was killed during the war. The US used it's cracking of the Japanese codes to decipher the itinerary of his review of the Japanese fleet in the Pacific and directed an attack against the planes carrying and protecting him, and shot him down at sea.
He is remembered for his caution that Japan not "wake the sleeping giant," that is, not attack the US and bring it into WW II.