If you've been at the company since the beginning and only took $36k/year (assuming in the US) with no equity and contributed lead engineering input, I'd consider you as part of the "founding team", if not a founder.
I'm aware that founders are generally those on the incorporation docs and everyone else is considered an employee in startup parlance, but I think first employees (especially as described in your case) take proportionally the same risk as the legal founders but get order or two magnitude less upside. It's a totally raw deal. Without knowing more, I'd be looking for 10%+ of founder-class shares if I were you.
Feel free to contact me (see my bio for contact info) if you'd like to discuss more privately. I'm going to be writing up something about this as well. I've seen first employees getting raw deals for years and it's always rubbed me the wrong way, especially as a founder and former "first employee".
edit: I want to point out that I'm aware equity, like many other things in business, is always about what you can negotiate. Post the seed round raise, your negotiating position is weaker than at the beginning, but my thoughts above are about what's "fair". What's fair and what's negotiable are often very different.
patio11 has a great take in the top comment here: https://news.ycombinator.com/item?id=2949323