Annamalai Ramanathan (29 August 1946 – 12 March 1993) was an Indian mathematician who worked in the field of algebraic geometry, who introduced the notion of Frobenius splitting of algebraic varieties in (Mehta & Ramanathan 1985). His contributions have led to the solution of many problems about Schubert varieties, such as the Demazure character formula.
Dr. Ramanathan, was a Professor of Mathematics at the TIFR in Bombay, India, and was a visiting Professor at the University of Illinois at Urbana–Champaign (1993). He has also been employed at University of Bonn and Johns Hopkins University. He was known for significant contributions to many areas of mathematics, including moduli spaces of principal bundles, Gauge theory, Frobenius splitting, the Demazure character formula, representation theory and the Verlinde formulae.
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.
Annamalai Ramanathan was third of four children born to a Tamil family S. RM. CT. Annamalai and Lakshmi. He got his B.Sc in Mathematics at Ramakrishna Mission Vivekananda College, and was recruited to attend TIFR, where he got his Ph.D. in Mathematics working with S. Ramanan, resulting in the publications. Ramanathan was crippled by adult onset polio in his late teens, and he used a crutch for the rest of his life.
During his tenure as a visiting professor at UIU-C, Annamalai Ramanathan died in Chicago, Friday, 12 March 1993, of complications following treatment for a heart attack, and is survived by his wife Vasantha, three daughters Lakshmi, Valli, and Priya, and a brother in Madras, India 
- Mehta, V. B.; Ramanathan, A. (1985), "Frobenius splitting and cohomology vanishing for Schubert varieties", Annals of Mathematics. Second Series 122 (1): 27–40, doi:10.2307/1971368, ISSN 0003-486X, MR 799251
- Ramanan, S.; Ramanathan, A. (1985), "Projective normality of flag varieties and Schubert varieties", Inventiones Mathematicae 79 (2): 217–224, doi:10.1007/BF01388970, ISSN 0020-9910, MR 778124
- Annamalai Ramanathan citation
- Ramanan, S., Ramanathan A. Some remarks on the instability flag. Tohoku Math. J. (2) 36 (1984), no. 2, 269-291.
- Ramanan, S., Ramanathan, A. Projective normality of flag varieties and Schubert varieties. Invent. Math. 79 (1985), no. 2, 217–224.
- Oral conversations, 1992
- Obituary posted online, at sci.math.research, https://groups.google.com/forum/?fromgroups#!searchin/sci.math.research/annamalai$20ramanathan$20dies/sci.math.research/gjq0hyMv1K4/fXGU-BNWsP4J%5B1-25%5D