there are plenty of fighters that you can pick from.
Fedor would be one of the top of my list.
A guy who was able to become the emperor, adored by almost anyone who saw his dominance in pride; respected and accepted as GOAT by 99% of fighters at that time as well, you don't get to become a personal friend of Putin by being obnoxious or dodging title shots.
If you want more names, we got the gracies (obviously). We wouldn't be watching MMA if not for them. I would even add Forrest & Bonnar. UFC wouldn't exist if not for them.
If you want to go in a different direction, like Silva & GSP who were responsible for the huge spark of popularity in US and around the world, you could go with them as well.
If you only want to go with popularity, I would go with Ronda, because not only she opened way for women in the UFC, but she actually had a fucking reign at the top, with multiple title defenses, and outside the cage, (even) Beyonce quoted her stupid quotes showing the level of influence she had.
And beyond that, there were plenty of fighters that were popular beyond the scope of MMA. The Nog brothers for example. Adored in Japan and the father of MMA for all brazilian fighters. You have Wandi, Vitor, Rua, etc... and in US, you have Guys like Randy whom his status in MMA is far beyond what he accomplished in the ring (heck his record is very unimpressive, but his status is as one of the greats mostly for who he was rather than who he beat) among many others...
I mean, If you think of Conor, he got a lot more flash than substance.
Undeserving title shots. No title defenses. Forfeited both belts. Lost to journeymen that had no camp, etc.
He is obnoxious and loud beyond everything, but that does not mean influential in MMA. Matter of fact, most fighters hate him, and he did NOTHING good for the game. If anything most of the things he changed were for the worse, and this is why I don't consider him to be (even close) to the top of the list.