Illapa is the Inca god of thunder, lightning and rain, and by the accounts of the Spanish chroniclers Bernabe Cobo and Cristobal de Molina he ranked third in the state cult after the creator Viracocha and the sun Inti, a ranking that reflects how completely Andean agriculture depended on the timing of the rains. He was pictured as a man in the sky holding a war-club and a sling: the crack of the sling is the thunder, the flash of his shining garment the lightning, and the rain the water he draws from the celestial river (the Milky Way, seen as a heavenly source of water) and keeps in a jar in the care of his sister.
Farmers prayed to Illapa for water, and in times of drought people were reported to tie up black dogs and leave them unfed so that their howling would call the god's attention to the people's need. Places struck by lightning were treated as huacas, sacred spots. The weather deity remains part of Andean religious memory, sometimes blended after the conquest with the figure of Santiago (St James).