I second Ken's comment. What you're describing is VP of Engineering or Product Development.
1. Are you planning on paying him/her?
2. If yes, how close to market rate?
Review similar listings on Angel.co to get an idea of the balance. In a funded start-up, 1% or thereabouts would be the norm. If the answer to #1 is no, then it goes up quite a bit and you have to ask are you "hiring" someone or bringing in a co-founder.