I could write pages on Sakamoto Ryoma but I will just list some of his high points and accomplishments.
Ryoma was a samurai from the Tosa domain. He abandoned his domain in 1862 to join the Loyalists fighting to restore the emperor to power, overthrow the Tokugawa Shogun and expel the foreigners.
In 1862, Ryoma decided to assassinate Katsu Kaishu. Katsu was a high ranking officer in the Tokugawa government. He was the commander of the ship "Kanrin-maru" on it's first mission to the U.S., sent by the shogun for the purpose of signing the Japan-U.S. commercial treaty. He was, perhaps, the most progressive person in the Shoguns government. His ideas on communicating with foreigners and his apparent support of the shogun aroused the anger of the Loyalists.
Katsu apparently knew of Ryoma's true intentions and persuaded him to listen to his views before taking any action. As Katsu later wrote, Ryoma did listen, admitted his true purpose, and said, "I am ashamed of my narrow-minded bigotry and beg you to let me became your disciple." After that, Ryoma introduced his friends to Katsu. It was an abrupt change in Ryoma's philosophy that led him to become a trusted mentor of Katsu. Katsu was convinced that Japan should have a navy for protection from other countries. But Katsu also knew that Tokugawa regime was weak.
Katsu persuaded the shogun to establish a naval school in Kobe. Katsu soon appointed Ryoma as a head of the new school.
In 1864, Japan continued to destabilize. The Choshu clan had bombed Dutch ships, the Satsuma clan had fought with the British at Kagoshima, and more assassinations had taken place. Later the two clans were attacked by a western allied forces. Satsuma and Choshu suffered humiliating defeats which forced them to realize the power of the west.
In 1864, Ryoma with about 20 friends started the "Kameyama Shachu" (the company) which would later become known as the "kaientai" (Naval Auxiliary Force). The kaientai is sometimes called Japan's first corporation. Ryoma modeled his corporation on foreign corporations with shareholders and investors. The company was used to aid Choshu and other domains with guns and other weapons to fight the Tokugawa.
Although Satsuma and Choshu were both rivals of the Tokugawa, they were also bitter rivals to each other. Ryoma began working hard to unite these to rival clans. He knew that if Satsuma and Choshu were united, they would be strong enough to defeat the Shogun. Ryoma finally realized his dream by convincing these two clans to unite in 1866.
The following day, Ryoma was staying at an inn where his girlfriend Oryo worked. The government learned of his negotiations with the two clans and sent soldiers to attack him. Over 20 soldiers broke into the house. Ryoma earlier had obtained a revolver and he used it against his attackers but his fingers were so badly wounded in the sword fight that he could no longer shoot. Ryoma escaped out the back and to safety at the Satsuma mansion in Kyoto where his wounds were nursed. After this event, Ryoma married Oryo.
In 1867, one of Ryoma's commercial ships was sunk negligiently by the Kii clan, who were relatives of the Shogun. Ryoma began negotiations with the Kii clan to try to secure funds for its replacement. Ryoma had become very familiar with international maritime law and Ryoma wanted this to be the first accident resolved by using maritime law in Japan. He succeeded in obtaining a rather large sum of money from Kii. The Kii clan was humiliated and Ryoma became famous.
Ryoma was now one of the most influential people in Japan, even though he was just a "lowly ronin".
Ryoma now believed that avoiding a bloody civil war was necessary to avoid foreign subjugation. He came to believe that the best plan to avoid war would be for the Shogun to relinquish power to the emperor peacefully. Ryoma told Goto Shojiro, a Tosa official, his idea and he in turn relayed it to the Tosa lord, who thus became the first to formally ask the Shogun to resign.
Ryoma's ideas for a new government were outlined in his Eight Point Plan. He suggested that power should be returned to the emperor and that the value of gold and silver be equalized with that of other countries. Ryoma made a list of the new government officials which was read by Saigo Takamori of Satsuma who wondered why Ryoma did not put himself on the list. Ryoma then told him, "I don't like the red tape and I have a dream that I will have business with western countries using my ships."
Stunningly, the shogun accepted Ryoma's plan to return his authority to the emperor in October of 1867. Sakamoto Ryoma's great efforts over the last five years led to the downfall of the Tokugawa Shogun, who's family had ruled for over 250 years.
In November of 1867, Ryoma was in Kyoto with his friend Nakaoka Shintaro. On the 15th they were both assassinated at a soy sauce shop called Omiya. Ryoma was 33. It was never proven clearly who assassinated Ryoma but many believe it was Kii domain in revenge for their humiliation in the ship sinking affair.
What was unique about Ryoma compared to many other leading men during this time in Japanese history, Ryoma thought of equality and freedom and he hated the class distinctions that existed in Japan.