Grandpa Meng is the lord of the Eighth Mountain and Sea. He is Meng Hao's grandfather on his mother's side. He is now one of the four Paragons of the Mountain and Sea Butterfly, alongside Ksitigarbha, Ke Jiusi, and Paragon Puppet Eegoo.
Soon after Meng Hao was born, Grandpa Meng bragged that his grandson would become a top expert in both the Ninth and the Eighth Mountain and Sea.
On his seventh birthday, Meng Hao experienced nirvanic rebirth for the first time. While Grandpa Meng was worried like everyone else, he didn't think this nirvanic rebirth was anything especially harmful. However, a similar scene played out on Meng Hao's second seventh birthday leading to widespread panic amongst the entire Fang Clan and the Meng Clan.
Soon after, the "Outsider" came and gave Meng Li and Fang Xiufeng a solution; however, no signs of either him or Fang Hehai were ever heard of. Although their life jades indicated that they weren't dead, they were, clearly, not in any position to return either.
It soon came to be known that he became the Eight Mountain and Sea Lord by the persuasion of Shui Dongliu, the so-called "Outsider". He was, however, almost never heard from despite having won the title Mountain and Sea Lord].
He became of the four guardians of the Mountain and Sea Butterfly, having raised his cultivation base to that of a 7-Essences Paragon. He later joined the fight for the extermination of the 33 Heavens and, along with Ke Jiusi, Paragon Puppet Eegoo and Ksitigarbha, cornered the Ninth Sea.
Meng Hao took Xu Qing along to visit Grandpa Meng at the Meng Clan to receive his well-wishes. Grandpa Meng advised Meng Hao to cherish Xu Qing as she waited for him for thousands of years.