He was born in
Munich into a family that was already experienced and successful in the trade of selling rare books. His great-grandfather Joseph Rosenthal was a lover of old books who ran an arts and antique shop. His great-uncle
Ludwig Rosenthal (1840–1928) became a successful antiquarian bookseller; Ludwig's younger brother
Jacques Rosenthal (1854–1937), Albi's grandfather, started out working for Ludwig and by 1895 had his own business. Jacques' son (1889–1981), Albi's father, earned a Ph.D. in art history and published extensively in this field. Working for the family business, he opened branches of Jacques' firm in
Berlin and
Lugano. Rosenthal later (1966) wrote of the trade of antiquarian bookselling and how, during the time of his ancestors in Germany, it had become far more scholarly and systematic in character: Not only the phenomenal spread of scholarship and bibliographical research, but also the demands and exigencies of a more methodical, 'professional' type of specialist collector and librarian are reflected in the personalities of the successful international booksellers at the turn of the [20th] century. The term 'wissenschaftliches Antiquariat'—'wissenschaftlich' meaning 'scholarly' rather than 'scientific'—became the hallmark of the leading firms in Germany. Their catalogues often included descriptions by eminent scholars of books and MSS. [manuscripts], and several of the antiquarian booksellers themselves became recognised authorities in their special fields. This description also characterizes the scholar-merchant role that Rosenthal eventually found in this field. Rosenthal described his father Erwin as "a distinguished art historian and a wonderful teacher". He reminisced: "During my schooldays at the
Wilhelmsgymnasium I went to his study in the evenings and we looked at books and pictures together. By the time I came to England, I was fairly well advanced in the study of art history." ==Career in England==