Name the deity from whom Mahisashur, the demon received the boon of immortality?

Explanation: Mahishasura was part demon and part Buffalo who was a tyrant greatly devoted to the deity Lord Brahma. He meditated for numerous years keeping in mind Lord Brahma. Lord Brahma upon seeing his devotion decided to pay him a visit and grant him a wish for his devotion. When Brahma finally visited him he decided to grant him a wish Mahishasura then asked for the wish of immortality.