No idea what the startup is or what you are trying to do, so no idea what you would need in a CTO or why you'd need one before you have anything else.
I worked for a startup where the president/founder of the company's friend created a single webpage for the company with a way to contact him. The domain name was good enough, so that was the start of the tech side. Hard to believe in this day and age, but that was the late 90s. After that, a (young) teenager wrote the webapp that ran the company's primary service. This person became the CTO, then was replaced by the former person who wrote the original webpage (that's right- just a page), but who was a Linux guru, could do the site, basically somewhat handled marketing, etc.
I recently read this:
http://onstartups.com/tabid/3339/bid/13808/The-Magical-Found...
which basically says the founders should be in this order:
1. Developer.
2. Designer / UI / UX person.
3. Inbound Marketer.
4. Sales Person.
One thing I can say for sure is that if you aren't technical and you are going to rely on someone you just picked up to basically run the engine of your company, you may just be dreaming.
If you have to pick anyone, make sure it is:
1. Not a friend
2. Someone you'd want to go camping with and vice versa (Sorry, I can't find the link for where that was suggested.)
3. A combination developer and server/networking geek. For a CTO this day and age in a startup, they should know Linux in and out, OS X in and out (seriously, a good sign is a macbook pro as client), know whatever your site is to be developed in (PhP, Ruby, Java, etc.), DNS, Apache, Passenger, Mongrel2, Tomcat, JBoss, etc. (depending on PhP, Ruby, Java, etc.), understand hosting and cloud services in current day and age, etc. They should live that stuff. There is no major for that. It is just a matter of interest and talent. It could be an English major.