Yamamoto Isoroku Admiral
From a strategic point of view I believe Japan was too hasty. Yamamoto was definitely a war planner, but he unfortunately did not plan for the A-bomb. Had they (Japan) taken some land (mainly China) and then waited, then things might have blown over, but like Hitler (did not only want Poland), they were not patient enough with one or two victories... they wanted more too fast!
As for Pearl Harbor, I found it strange that the navy did not get more planes in the sky with a whole hour of time to their advantage.