Definition of founder

I am looking for people's opinion on definition of "Founder" of a company.

Here is the background:

I founded a company in May 2002 and hence I was the "founder" of
the company. When I founded the company I had a few employees
as I raised some seed funding.

In December 2002 a friend joined me. He is a great worker and
contributed in a major way. As we were running out of money, for
a few months he worked for no or little money.

He finally asked me if he can be a co-founder of the company.
I was OK him to be "co-founder" because of his contributions, however 
I do not want to give up my "founder" status.

Any and all thoughts are appreciated.

(As entrepreneurs most would understand the importantace of this
intangible satisfaction of being a founder)