Is there an alternative title to founder?

In the past I thought titles were silly little trinkets for the ego (still do for the most part), but have learned that they can be important in terms of establishing credibility with people you don't know, etc.

About 10 years ago, I started with a startup about a month after their founding, there was only one other developer who was to be frank terrible, did a ton of sweat equity work to the point that I was working for free for a number of months, but never bothered to stake claim to a title. The company eventually sold for $500MM. I came out with a very healthy exit given the sweat equity, but don't have my name associated with it as, say, CTO, which in effect I was for about 18 months.

Now, I've become involved with a startup. I have about $100K in the seed round of $500K, am working full time as the only programmer. Since I'm not one of the guys who actually started the company, I don't feel I should call myself a founder. I was there pretty much day 1, though, and working as if I were a founder. I'd like to make sure I stake claim to a title this time, but am not sure what it would be.

Thoughts?