Rupert Willis was born in Yarram, Victoria, the son of a bank manager whose wife was the daughter of a congregational minister. He was educated at home by his parents until the age of ten and later attended Melbourne High School and the University of Melbourne. He graduated MB BS in 1922 in the same class as Roy Cameron and Macfarlane Burnet and then spent several years in general practice in Tasmania before being appointed medical superintendent of the Austin Hospital, Melbourne in 1927. The Austin was then a hospital for cancer and incurable diseases and here, with no formal training as a pathologist, Willis began his post mortem studies of cancer and developed his interest in the behaviour and morphology of tumours in man.

He was appointed pathologist to the Alfred Hospital, Melbourne and lecturer in pathology of the University of Melbourne in 1930. Except for 1933 and 1934 spent in London with Sir Arthur Keith at the Royal College of Surgeons he remained there until 1945, when he returned to London as professor of pathology at the Royal College of Surgeons. Three years later he moved to the Royal Cancer Hospital, London and in 1950 succeeded Matthew J Stewart as professor of pathology in Leeds.

In 1955 Willis developed an illness, misdiagnosed as cancer, resigned his chair prematurely and returned to a small village in Cornwall. Here he continued experimental work in a laboratory in the back garden of his cottage and for many years received a stream of problem cases sent for his opinion from all over the world. His tumour reference collection, based on 8,000 documented and personally studied cases, is now in the department of pathology in Leeds. In 1962, soon after the death of his wife Margaret, his devoted companion and assistant in most of his work, Rupert moved to Cheshire to live with his daughter and her husband and remained there until his death in 1980.

Although he published over 140 papers, Willis's major contributions were made in textbooks: The spread of tumours in the human body (1934, 3rd edit. 1973) and The pathology of tumours (1948, 4th edit. 1967), both of which are regarded as classics; The borderland of embryology and pathology (1958, 2nd edit. 1963) and The pathology of tumours in childhood (1962). Willis made an immense contribution to human tumour pathology. His clearly expressed, concise and often dogmatic views had a profound influence on a generation of histopathologists and helped to formulate modern concepts of tumour histogenesis and classification.

A small, brown faced man with great personal charm, Rupert Willis had many interests, including music, botany, petrology, ceramics, photography and philately, which he delighted to share with friends of all ages. He had an abiding curiosity and enthusiasm for the collection and classification of many different sorts of things. His younger brother Jim, a highly distinguished botanist, had a very similar approach and enthusiasm and one suspects that the behaviour of both reflects their early education by perceptive parents in a small country town.