Mary Ann Horton

''This article is about the software developer. For the archaeologist, see Mark Horton (archaeologist)''

Mary Ann Horton, formerly Mark R. Horton, was a Usenet pioneer. Horton co-wrote the B News server software. Horton worked at Bell Labs for twenty years.

In the early 1970s, Horton designed and implemented the HORTRAN compiler. He was an expert user of early networked computing systems, such as the HP 2000 minicomputer, and provided fellow students with valuable advice that led many to lifelong careers in computer science and related fields that rely heavily on computing.

Horton wrote a FORTRAN implementation of John Horton Conway's Game of Life on a UNIVAC 1108 and tracked the evolution of thousands of cellular automata patterns on grid spaces up to 1000 by 1000, using magnetic tape to store intermediate results.

Horton is transgendered (bi-gendered), and until 2001 freely presented as both Mark and Mary Ann.