Moonglow is a female yak and the mother of Brian (also known as Brainy-Yak).
Before Professor Moshimo became the world-renowned scientist, he was a yak farmer in the Mexican Alps. Moonglow is one of his most beloved yaks and his best milker.
One day, while waiting in line to be milked, she snuck away from the group. When Dave wants to bring her back, Moshimo stops him and goes after her. He then discovers that she is giving birth to Brian and he helps her with the process.
Moonglow was very proud of her newborn son and didn't care that he was dumb and clumsy. She showed sympathy for him when the other yaks made fun of him. She entrusted Moshimo to give Brian super-intelligence via brain surgery. Despite the drastic difference, she remained a caring mother to him.
However, Brian despised Moshimo for turning him into a freak, which led to his decision to run away from the farm, but not before leaving a bittersweet goodbye note to Moonglow, whom he was saddened to leave behind.
When Dave comes to Kaziland to bring Brian back, he reveals that his mother was waiting for him and wanted to see him.