Vatapati and Ilvala

Two demons who took revenge on Brahmins by Ilvala turning his brother into a goat and serving his meat when a Brahmin came to visit. After the meal, Ilvala said a mantra and Vatapati became the goat again. The brahmin died. Sage Agastya vanquished them.

Read about Vatapati and Ilvala here
http://sushmajee.com/biographies/bio-V-Z/vaataapi-ilval.htm