Sakamoto Ryoma is often portrayed in the Japanese media for his role in attempting to overthrow the shogunate during the Bakumatsu period. Since he was assassinated when he was still very young, the Japanese media are very sympathetic to his cause. I wonder how much of a role did he actually play in overthrowing the Tokugawa regime?
It is true that Sakamoto Ryōma died young, and his heroic role is perhaps overly dramatized today (especially the famous story of his aborted assasination attempt of Katsu Kaishū), but his considerable reputation as one of the most important figures in bringing down the Tokugawa is not without merit. The two most important moments where he, as an individual, becomes a particularly important figure in the Meiji restoration:
The classic English source on this is Marius Jansen's work, frequently read by students of Japanese history: Sakamoto Ryoma and the Meiji Restoration