I was lucky to be brought up in a household where artistic creativity was taken for granted as simply part of everyday life. My parents, Robert and Elizabeth Munn, were both painters, he in watercolours, she in oils. Though neither was able to pursue a professional career as an artist (he was a railway official, she a teacher), they both worked to a high standard. As young adults both had been elected members of Paisley Art Institute, whose ranks included at one time such luminaries as Sir Muirhead Bone and Sir John Lavery. ... Douglas (my senior and only sibling) had a distinguished academic career as a "pure mathematician" - the kind, he would engagingly explain, who functioned with pencil and paper, and whose intellectual undertakings had no practical application whatsoever (but had a strong aesthetic content). My earliest memories are of his accomplished piano playing; already in his early teens he was composing piano music, much influenced by Chopin and hauntingly melodic. His music became more astringent as he grew older. A selection of his compositions is lodged in the Scottish Music Centre in Glasgow.

In the classical theory of representations of a finite group by matrices over a field F, the concept of the group algebra (group ring) over F is of fundamental importance. The chief property of such an algebra is that it is semisimple, provided that the characteristic of F is zero or a prime not dividing the order of the group. As a consequence of this, the representations of the algebra, and hence of the group, are completely reducible. In the present paper we discuss a more general concept, the algebra of a finite semigroup over a given field. Our main task is to find necessary and sufficient conditions for such an algebra to be semisimple, and to interpret some of the results of this investigation in terms of representation theory.

I should like to express my gratitude to Dr D R Taunt for his encouragement and extremely helpful criticisms, and to thank Mr D Rees for suggesting in the course of conversation the result of 4.7. I am also indebted to the Carnegie and Cross Trusts for grants.

Douglas took the signing of the Official Secrets Act extremely seriously and never himself revealed anything of his work there. Such information as we have has been provided by GCHQ itself. He spent most of 1955 there, returning as a consultant once or twice each year for periods of up to three months at a time until 1963. He even established sufficient seniority to be eligible for 1st class (as opposed to 2nd class) rail fare to and from Troon, a true indicator of success when in government service! However, it was serious business at GCHQ, which describes itself on its web-site as "an intelligence and security organisation". It boasts of having discovered trap door functions, public key encryption and what is now known as RSA encryption, the main underpinning of the security of internet transactions, several years before such schemes were openly proposed in the USA. From discretionary release of retained GCHQ records by the GCHQ historian, it is evident that Douglas was engaged in "trying to push the art [of using computers] to the limit and consider the limitations of the [then] present [computers] and [the] requirements of future computers". His work "engaged mathematical problems and problems that fringed into mathematical logic". He understood the engineering limitations of the machines of the day and how to get around their logical constraints. It seems fair to say that his GCHQ activities kept him at the leading edge of computing developments.

... in 1966 he was appointed to the chair of mathematics in the fledgling University of Stirling, by which time he was also a Fellow of the Royal Society of Edinburgh. I followed him a year later, and for the session 1967-68 we were the mathematics department. We were the music department as well: no provision had been made for music, and the two of us had to take action. Munn, leading from the front, gave great encouragement to talented students in organising chamber music. I conducted a choir - with Munn as one of my basses.

When I entered first year at Glasgow University, I was already interested in mathematics, but just as interested in physics and chemistry. Douglas was one of my first year instructors and the contrast between his lectures and those in the other courses that I was taking was like night and day. He brought the same preparation and clarity to his undergraduate lectures then that he still demonstrates in his conference presentations. I have no doubt that that experience was an important factor in my subsequently choosing mathematics over the other sciences and for my later choice of Douglas as a supervisor.

The meticulous care with which he prepared his lectures was typical of how he approached all his tasks, especially the reading and writing of papers. Any paper that he read was considered in the minutest detail for every grain of insight that could be gleaned from it. Each of his own papers would go through many rewritings before reaching a level of presentation that he found acceptable. This was great training for a student and taught me the value of understanding papers thoroughly, not just the stated results, but also the why and the wherefore of their workings.

On visits to Troon, we would occasionally go for walks among the dunes along the front there. It seemed a great place to go when struggling with a piece of mathematics. However, he always gave me the impression that he did his best work on the train going up to Glasgow and back. I think that he did it in the margins of the Glasgow Herald!

He published over eighty highly influential papers on semigroups and their algebras. Munn algebras, Munn graphs and Munn semigroups, just three of his many ideas, are known to all who work in these areas. His papers were renowned for the clarity of their exposition. He would revise them and polish them like a jeweller cutting and polishing a precious stone. He would not be satisfied until the results were optimal and shone to best advantage. His lectures, whether to research conferences or first year calculus classes, were similarly well crafted and shaped. His papers and lectures set a standard to which we all could aspire. The main focus of his work was on semigroup algebras and matrix representations of semigroups, though he also developed a strong interest in the more purely algebraic theory of semigroups about which he wrote many influential works. His very first published paper concerned semisimplicity of semigroup algebras. By that time, he had met Gordon Preston who told him about the class of inverse semigroups and Douglas's second published paper was about the axioms for inverse semigroups and appeared in the very same volume of the Proceedings of the Cambridge Philosophical Society as his first paper. This second paper was a joint work with Roger Penrose (later Sir Roger Penrose), who was interested in generalised inverses of matrices at the time. Both themes (semigroup algebras and abstract theory) persisted in his work until his last few years when his interests seemed to return once again to his first love in semigroup algebras and he enjoyed a successful collaboration with Michael Crabb.