He is best known for coining the term "Regality Theory" and for writing extensive optimization manuals for machines running the x86 architecture.

[1][2] Agner Fog is the main investigator of Regality Theory, the proposition that the environment a group is in selects for certain psychological traits.

[2][4] He maintains a five-volume manual for optimizing code for x86 CPUs, with details on the instruction timing and other features of individual microarchitectures.

This is a high performance open source CPU Instruction set architecture with variable-length vector registers.

[8] Fog has written a few pseudorandom number generators with a variety of distributions, with a focus on performance (SIMD) and correctness with regard to floating-point behavior and statistical properties.