Professor Jim Geelen is already a world leader in the areas of combinatorial optimization and matroid theory. The referees describe him as an "outstanding talent" and a "very creative and original researcher" with a "huge international reputation".
The following are among the highlights of his 30-odd papers. With Gerards and Kapoor, he characterized the matroids representable over the finite field GF(4), which had been considered an impossibly hard problem. Their paper is described as a "huge breakthrough". With Whittle, he has proved that among the set of excluded minors preventing representability of a matroid over a given finite field, there is only a finite number of matroids of a given branch-width. This is remarkably strong evidence in support of the Rota conjecture.