(Aad Granth Sahib - Page 1329)
In many publications, both books and websites, it is many times mentioned that the Gurmukhi Scripture used to record Gurbanis was invented by The Second Master, Sri Guru Angad Dev Ji.
But if one takes a closer look, there would be no doubt left that it was Sri Guru Nanak Dev Ji who invented the Gurmukhi characters though it was spread and made well known by the Second Master.
As mentioned in the Janam Sakhi, Guru Angad Dev Ji Said that in order to compose more GurBanis, He would require a person who has the knowledge of both Bidhachari as well as Gurmukhi. Only then was Bhai Paeda Mokha discovered at Sultanpur who already had the knowledge of both scriptures.