Theo Geerinck (The Hague, 1942) studied at the Royal Naval Institute and at Delft University of Technology in the Netherlands. He retired from the Navy in 1994 as Director of Naval Research. Since then he is occupied with two aspects of recreational mathematics.

He collects, designs, and produces mechanical puzzles. As a member of the "Nederlandse Kubus Club" (Dutch Cubists Club) he is one of the editors of the club's newsletter, Cubism For Fun. He participated several times in the Exchange of the International Puzzle Party, where around a hundred puzzle-collectors and -designers from all over the world swap their latest puzzles.

His other activity is the design of geometrical objects, most of them loops and knots. These closed "curves" in space are composed of pieces of straight beams and in general follow a path on a polyhedron. The challenge is to use similar building blocks. Experiments are performed in virtual space, changing variables as the crosscut of the beam (circular, triangular, square, and rhombic), the type of connection and the proportion between volumes of space and material. Afterwards, a prototype is realized in some hardwood. Most objects can be scaled upwards and/or produced in other materials.

Activities on puzzles and geometrical objects tend to interrelate. Sometimes geometrical objects composed of more elements are so hard to assemble that they function as a beautiful puzzle. On the other hand, objects designed as a mechanical puzzle have aesthetic qualities that justify exposition as a work of art.