From the website of Bevis Marks Synagogue (under the section, "The Rabbis and Famous Sons):
Of the numerous Hahamim (literally, wise men) who have been Chief Rabbis of the Spanish and Portuguese Congregation, at least three have been widely famous. . .
Moses Gaster (1856-1939) was Haham of the Congregataion from 1887 until 1918. Dr. Gaster was an Ashkenazi by birth though his own family had always worshipped with the Sephardim and was thus the only non-Sephardi Haham. Born at Bucharest in Rumania, in 1885 he came to England, and was appointed Lecturer at Oxford on Graeco-Slavonic Literature. In 1887 he was offered, and accepted, the office of Haham.
In addition to his great scholarship covering many fields both religious and secular, he was one of the fathers of political Zionism in Great Britain and worked ceaselessly for the time when this country (UK) would recognize the demands of the Zionists. His efforts eventually bore fruit when the original draft of the now famous Balfour Declation was prepared in his own home at No. 193 Maida Vale, London, W9.
Gaster's remarkable gifts did much to raise the standing of the Congregation, for he was undoubtedly the most versatile and eminent holder of his office since the days of David Nieto.
There is a portrait of your Great Grandfather on the page! Finally, there are more than 69,000 entries on Google for Moses Gaster . . . Enjoy!
I hope this helps!
