21st May, Saturday, is Nammalwar Tirunakshatram (Birthday). He is the 8th alzhwar out of 12 alzhwars very well known for his many hymns on devotion to Vishnu. Details about his birth star, place etc are available here.
Contributions of What Nammazhwar or Nammalwar:
Nammaazhwar contribution of 4 works which can be compared to all Vedas(numbering 1296 hymns) to the 4th thousand of the Divya Prabhandham includes the entire 4th thousand and part of the 3rd thousand.