Karna is one of the most admired characters of Mahabharata. He is loved by us for multiple reasons. Generosity, dedication to friend being some of them. But lot of pity him, because he lived like a "sutha putra" though he was actually a king. We lovingly call him Dhana shoora veera Karna.
Our Hindu calendar also has given this man a place.
Karna went to heaven after his death. He was treated royally there. But for food he was given only gold, pearls and precious stones. He asked for some edible stuff and the reply was surprising. "During your stay on earth, you never gave food as dhan. You always were generous enough to give gold and ornaments. Others atleast do the shraddh and give food on that day. You have not even done that. What you give on earth is what you get in heaven."
Karna explained his situation. "I never knew that food charity was most sacred. And I never knew who my parents or ancestors were. How could I perform shraddh? When I got to know my parents and ancestors, I died."
Hearing this valid argument, the authorities at heaven made an exception. They allowed Karna to go back to earth for 15 days. In these 15 days, Karna performed the shraddh of his ancestors and did anna(rice) dhana to a lot of people.
These 15 days are known as pitru paksh in the Indian calendar. This is the period when Hindus perform special functions as a tribute to their ancestors.
Karna's place in calendar is etched for times to come.
PS- Pitru Paksh will start in 3 days from now. It will end with Mahalaya Amavasya.