There are many stories of his brilliance and his novel approaches to kabbalah which solved problems which had the best of the generations stumped. According to one well known kabbalist in Jerusalem, he understands the Etz Chaim better than R' Chaim Vital (who actually wrote it, and heard the shiurim from the Ari himself).
There is also a tradition that any prayer said at the graveside of the Rashash will not go unanswered. He is buried on Har HaZeitim, so I imagine it will be packed there today.
May His Soul be Bound in the Bonds of Eternal Life
This is part of the entry of what wikipedia has to say about him:
Sar Shalom Sharabi (Hebrew: שר שלום מזרחי דידיע שרעבי), also known as the Rashash, the Shemesh or Ribbi Shalom Mizraḥi deyedi`a Sharabi (Jewish Sharab, Yemen 1720 - Jerusalem 1777/ (10 shevat 5537)), was a Yemenite Jewish Rabbi and Kabbalist. In later life he became the Rosh Yeshiva of Bet El Yeshiva. He was one of the Jewish world's foremost masters of Kabbalah, Torah, Talmud and Halacha in the 18th Century, and one of the first Yemenite Jews to have a major influence on the wider Jewish world. He is now considered to rank among the Acharonim and to be one of the most important Mizrahi Rabbis in history.
He is primarily known as a Kabbalist, but his rulings on Halakha (Jewish law) were and still are considered to have high authority, particularly among Yemenite Jews, but to some extent among Jews world wide. He was also a pioneer of Talmud Torah schools in Israel and Yemen, Warrior on behalf of the Old Yishuv and a leading Merchant in the Middle East. He was also a Jewish Sexton for many properties in Jerusalem, Israel.
Sharabi's son Yitzhak Mizraḥi Sharabi (d. at Jerusalem in 1803) bore the same high reputation for piety as his father, whom he succeeded as Rosh Yeshiva of the Bet El Yeshiva.