#### One of the greatest British mathematicians of his generation, he created the renowned maths department at Warwick University in the mid-1960s

Sir Christopher Zeeman, who has died aged 91, was one of the true greats of British mathematics. His finest memorial is the department he created in 1964 at Warwick University, housed in what is now called the Zeeman building. Warwick is now firmly ranked among the top mathematics departments in Britain; and its mathematics degree programme was recently assessed as No 13 in the world.

When he joined the fledgling university, he concentrated initially on three core areas of mathematics, algebra, analysis and topology, inviting several key figures to join him in the new venture. Legend has it that they all declined, so he wrote to each of them saying: "That's a pity, the others have all accepted." Christopher never denied this.

I still have vivid memories of arriving at Warwick in 1967 as a new PhD student, when there were only 600 students in the entire university. The Mathematics Research Centre was already attracting several hundred top mathematicians a year from all over the world. It was an exciting place to be.

Christopher had a charismatic personality enhanced by an impressive beard. He could be a little intimidating the first time you met him, but he was friendly, generous and tireless in his drive to encourage the growth of new mathematics. He was also unusually active in public engagement: talking to schools, giving public lectures, appearing on the radio. As a result, Warwick never developed the attitude that such things were beneath the attention of serious academics.

In 1978, he delivered the Royal Institution Christmas Lectures on BBC television. This lecture series, founded by Michael Faraday in 1825, focuses on enthusing young people about science; Christopher was the first mathematician to give the lectures. The topics included boomerangs and gyroscopes, perspective drawing in art and catastrophe theory.

Christopher was born in Japan, but his parents moved to the UK when he was a year old. His mother, Christine, was British; his father, Christian, was Danish. Christopher attended Christ s Hospital, an independent school in Horsham, West Sussex, and was a flying officer in the RAF between 1943 and 1947. He then went to Christ s College, Cambridge, remaining there to study for a PhD under Shaun Wylie. The subject was topology, a branch of mathematics that came to fruition in the early 20th century and has since become a core topic in the subject.

"Topology," Christopher said in a broadcast on " the scientist's toolkit" on the BBC Third Programme in 1967, "is a sort of geometry." But it is flexible geometry in which lengths and angles can be changed by any deformation, subject only to preserving continuity. His discoveries in this area included unknotting spheres in five-dimensional space, and the engulfing theorem, which has been used to prove special cases of the Poincaré conjecture. This conjecture characterises high-dimensional spheres in a very simple manner. It dates from 1904 and was proved in full by Grigori Perelman in 2003.

In the early 1970s, Christopher came across some provocative ideas of the French mathematician René Thom, on a new way to think about mathematical models of reality. Among Thom's suggestions was a list of "catastrophes élémentaires" a topological classification of sudden changes. This so appealed to Christopher's mathematical inclinations that he changed his research field from topology to what soon became known as catastrophe theory.

He invented a "catastrophe machine", in which a circular disc on a pivot was attached to two elastic bands, one with a free end. As that end moved around, the disc would suddenly flip to a drastically different position, a vivid example of discontinuous behaviour resulting from a continuously changing cause. Catastrophe theory, renamed singularity theory, has now established itself as an important technique in many applied areas. One of Christopher's early proposals, a "clock and wavefront" model demonstrating a key stage in the development of a vertebrate, was recently shown to be correct.

He was elected a fellow of the Royal Society in 1975, and was president of the London Mathematical Society, the UK's major pure mathematical professional body, from 1986 until 1988. In 1988 he left Warwick University and became principal of Hertford College, Oxford. From 1988 to 1994, he was professor of geometry at Gresham College, giving 12 free public lectures a year.

In 1991 he was knighted for "mathematical excellence and service to British mathematics and mathematics education". The Institute of Mathematics and Its Applications and the London Mathematical Society jointly set up the Zeeman medal in his honour, for activities in public awareness of mathematics.

He is survived by his second wife, Rosemary (nee Gledhill), whom he married in 1960, and their three sons, Tristan, Crispin and Sam, and two daughters, Mary Lou and Francesca; and by a daughter, Nicolette, from his first marriage, to Elizabeth Jones, who predeceased him.

**Ian Stewart**

*Erik Christopher Zeeman, mathematician, born*4

*February*1925;

*died*13

*February*2016

24 February 2016 © Guardian News and Media Limited