Gordon gorefist is one of the possible first bosses. One of the amazing things about Remnant is that it switches up the bosses and maps as you run through the game. In this run through I had a different first boss that fires arrows and teleports.
It’s not strictly procedural I think, but there’s a lot of ways they use to make it different for each player. I’ve just started a run through adventure mode in the Earth “biome”, which is a separate mode you can switch to with your existing character that doesn’t affect story but allows you to go back in to an area to try and find something you missed first time.
For example, the helmet that finishes off my armour set is only found on earth but I missed it in story mode. So I’m looking for it now in adventure mode and if I still fail (all the while levelling up) I can re roll adventure mode again until I get it.
The thing is, in the process of doing that I’ve found two later stage bosses on earth (one in story, one in adventure) that I didn’t know existed. And I played a lot of hours of this up until now. Like a LOT.
Re: boss not being there. It may have glitched, or died when you died. Can you go back to the hub and exchange anything with the grumpy mechanic lady? She generally converts boss rewards into amazing weapons. If you can, you’ll know you killed him.
If not and you feel you’ve missed out you could either begin again (won’t take long at all at this stage) or roll adventure mode to try get any gear or bosses you want. It’s not guaranteed to be him again but you can keep trying until you find him.
Re: armour. Yes gear is essentially your class. You’ll probably find that you switch a few times as you find new cool armour and weapons.