Answer
The answer is Ashikaga Yoshiaki, the 15th and final shogun of the Ashikaga shogunate. Nobunaga's victory over Yoshiaki in 1568 led to the establishment of Nobunaga's control over Kyoto, which was then the political and cultural center of Japan. This marked a crucial turning point in the Sengoku period, paving the way for the subsequent unification of Japan under the rule of Nobunaga and his successors.