MLPF does not have an owner.
IP.B counts the initial Admin account as the first user that is Feld0. Note that he was the owner at the time but has since retired that role and authority legally and in practice as Poniverse is a Canadian NPO. So he most certainly counts as the first user as he is not actively a member of staff. Kurtiss was next and he is the cofounder. The following one who joined is found here.
Question correctly answered. Closing