Fatunla was born in 1943 near Igede-Ekiti in what is now Ondo State, where he attended the Baptist High School from 1956 to 1961. After a year at college in Ijebu-Ode he took a degree in Mathematics at the University of Ibadan in 1965-68. There followed three years with Mobil Oil in Lagos which laid the foundations of his formidably professional computing skills; then his first period of overseas research at Loughborough University of Technology under Professor David Evans, completing a PhD in Computer Studies in 1975.
Fatunla's career as teacher had already begun: by 1969 he had had two spells schoolteaching in his home town and one in Lagos and he combined his PhD with a year as a lecturer at the university in Ile-Ife.
Fatunla knew his own powers and the value of developing them by international contacts. His charm, energy and determination to be based in Nigeria and contribute to the academic growth of his country won him friends world- wide. He travelled extensively to conferences, and to research visits in Illinois, 1977, Dublin, 1981 and 1988, Simon Fraser University, British Columbia, 1990. From 1984 he was Head of Mathematics at Benin University (Uniben). His widening reputation was recognised by a 1993 Distinguished Leadership Award of the American Biographical Institute and brought responsibilities in other developing countries: external examiner, Nairobi; guest conference speaker in Delhi and Tehran; setting up an Industrial mathematics MSc in Mauritius.
His main personal research was in numerical methods for stiff and oscillatory ordinary differential equations, in which many students at Benin followed him. But his view of priorities in a developing country led him to teaching and exposition. In 1983, and biennially from 1986, he led the now famous Uniben Scientific Computing Conferences. At first almost single-handed, then with a growing support group at Uniben, he attracted funding and impressive teams of overseas speakers, and edited the Proceedings. Since the 1988 conference these have been typeset and printed in Nigeria, latterly by the Ada/Jane Press which he founded. He found time to write two fine textbooks, Numerical Methods for Initial Value Problems in Ordinary Differential Equations (1988), a best-seller on Academic Press's list, and Fundamentals of FORTRAN Programming (1993). Widely adopted by Nigerian universities, the latter is both up-to-date and adapted to African needs.
His death occurred the week before he was due to address the Computer Association of Nigeria on "What Parallel Computing is All About" at their annual international conference, when it was widely expected that he would be elected president of the association.
As well as immense appetite for work - like many high achievers he needed little sleep - Fatunla had great zest for enjoyment, and many friends will remember sitting down to beer, political discussion and television after a day of conference, or enjoying pepper soup and bushmeat at one of his clubs.
Simeon Olujuyigbe Fatunla, mathematician: born near Igede-Ekiti, Nigeria 5 September 1943; Head of Mathematics Department, Benin University 1984- 95; married 1971 Grace Itiola (four sons, one daughter); died near Auchi, Nigeria 19 May 1995.