In Hindu mythology, Vena was a great king. However, he became evil and corrupt. The world became so gloomy and dark that the earth-goddess Bhumidevi decided that she would not provide crops to humans anymore. She took form as a cow and went into hiding. Meanwhile, a group of Rishis killed Vena out of anger. They then rubbed the thigh of his corpse, and took out all the evil from his body. Afterwards they rubbed Vena's arm, and the good Prithu emerged. This being was Vishnu incarnate, and as soon as he was born, Vishnu's Sharanga bow fell from heaven into his hands. However, Bhumidevi still refused to give crops to people. As soon as Prithu, son of Vena, threatened to kill her, she gave in, but in return Prithu would be her eternal guardian. This is why Bhumidevi is also known as Prithvi.
In the Rigveda (10.123), Vena is a personification of a celestial being, perhaps the rainbow. The name of the hymn is also Vena, as is the name of the author of RV 9.85.