Mark Bonnin was the third in a family of five sons and two daughters, born to James Atkinson and Winifred Bonnin (nee Turpin). His father was a qualified surgeon (FRCS) who also practised as a general practitioner. Like his four brothers, Mark had obviously inherited the genes of considerable height, being well over six feet tall. Mark's secondary schooling was at St Peter's College, Adelaide. Following this, he graduated in Medicine at the University of Adelaide in 1936. He was proficient in many sports and was awarded blues for rowing and lacrosse at the university.

Internship at the Royal Adelaide Hospital (RAH), was followed by postgraduate training in internal medicine at the Central Middlesex Hospital, London, in 1938 and 1939. He passed the MRCP examination in 1939. His intention to undergo further training in the UK was interrupted by the outbreak of World War II. He hurried back to Australia to enlist in the Australian Army Medical Corps, which embarked not long after his return for service with the Australian Imperial Force in the Middle East. During this period, he rose to the rank of Lieutenant Colonel in charge of the medical division of the 2/6 Australian General Hospital, and was mentioned in dispatches.

After several years of service in the Middle East and adjacent areas, his unit returned to Australia for a period of reconditioning, and while he was stationed in Western Australia, Mark met and married a nursing sister, Avis Watts. They had four children, a son and three daughters. As an indication of abundant energy and excellence, it was during this time in Australia in 1942, that he studied for, and passed, the MRACP examination before service in the South West Pacific area. Military service ended completely in 1946, and he was appointed as an honorary assistant physician to the RAH in 1947, having passed the MD examination of the University of Adelaide in 1946.

From the time of his appointment until he retired from the hospital staff at the compulsory age of 65 years, Mark Bonnin taught and trained medical students and postgraduates at the hospital, and outside it, in a superb and compelling manner. His outstanding expertise in these areas, and his overall excellence, was recognised after his retirement by the Medical School's award each year of the Mark Bonnin Prize to the best tutor in Internal Medicine. His last years at the hospital that he loved were served as its senior physician, and he was honoured as an emeritus visiting physician on his retirement.

He continued his private practice as a consultant physician after hospital retirement, being sought widely by patients and his colleagues in practice for referrals. His dedication and contributions to the sick were outstanding and continued until he retired from practice completely in the late 1980s. He kept abreast of new knowledge, and was an enthusiastic and excellent treating physician of the modern era, being an avid reader of many medical journals, and very positive in his approach to therapy. This breadth of knowledge encompassed all the disciplines in internal medicine.

Mark Bonnin loved the challenges and science of internal medicine and especially the RACP, which he served with distinction and dedication for over 20 years. He was a member of the Board of Censors from 1957 to 1967, a member of Council from 1964 to 1973, and at the same time, Chairman of the South Australian State Committee. These services, his outstanding ability and his contributions to so many College and other committees were recognised by his College with the award of the College Medal in 1984.

Outside of his professional responsibilities, this tall and imposing man had many different interests. His manner was firm but gentle, measured in his speech and with a broad sense of humour. He enjoyed good wine and food like his brothers, but kept himself lean and fit. He was an ardent conservationist, with a great expertise since his undergraduate days in ornithology, achieving a national reputation in this field. Many of his fine photographs adorn books on Australian birds. With the easing of some professional responsibilities in 1997, he was able to devote even more time and influence in conservation areas. He was the founding father of the National Parks Foundation of South Australia, of which he was the first president from 1981 to 1986. A number of reserves and conservation parks in South Australia exist because of his plain speaking, his efforts and strength of purpose. It is not surprising that his dedication and contributions professionally, and outside this, were recognised by the award of Member of the Order of Australia in 1989.

Sadly, a fatal illness in his last two years ended the life of a remarkable man who will be remembered as a compassionate and caring person with a great zest for life, and a spur for high achievement.