Notatus of Bonisagus
Notatus of House Bonisagus, the Founder's second apprentice, was the first primus of the House. Through a major breakthrough, he invented the Aegis of the Hearth, a ritual not wholly incorporated into Hermetic magic, but that can be cast by any magus (who is otherwise not prohibitted from casting rituals generally).
Publishing history
Notatus wasn't mentioned in write ups on the houses, such as Order of Hermes or Houses of Hermes but as far back as the Third Edition he was named in the Aegis of the Hearth spell description, where it was noted that he was made primus for inventing the spell.