[samsheen]

If I had to look for one single thing in a CTO to head my new startup - it would be a person who is able to answer - "No. I don't know how to do that. But I will figure it out and let you know".

Since you mention that you are a startup, you will have technical issues that no one single person will have worked on before. Instead of looking for someone who has UI, backend, server admin, mobile, web [add many more] skills, look for someone who is honest about what he knows and does not know, is not intimidated by different technologies and enjoys getting his fingers wet in different areas of work. I'd go with a Jack of all trades to a Ninja-Guru-Shaman programmer any day.