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.