Annamalai Ramanathan (29 August 1946 – 12 March 1993) was an Indian mathematician in the field of algebraic geometry, who introduced the notion of Frobenius splitting of algebraic varieties jointly with Vikram Bhagvandas Mehta in (Mehta & Ramanathan 1985).
The notion of Frobenius splitting led to the solution of many classical problems, in particular a proof of the Demazure character formula and results on the equations defining Schubert varieties in general flag manifolds.
Ramanathan made significant contributions to many areas of mathematics, including moduli of vector bundles, Gauge theory, algebraic geometry in positive characteristic and representation theory.
The Council of Scientific and Industrial Research awarded he and his collaborator Vikram Bhagvandas Mehta the Shanti Swarup Bhatnagar Prize for Science and Technology (the Indian Presidential award for achievement in the mathematical sciences) in 1991 for his work in algebraic geometry.
During his tenure as a visiting professor at University of Illinois at Urbana-Champaign, Ramanathan died in Chicago, Friday, 12 March 1993, of complications following treatment for a heart attack.