rockstar easily. i wonder what open world games would have been like if they never existed?

rockstar in my opinion. They created the utopia of gaming in my mind and cornered the open world games market,in my opinion.

I'd say it's probably between
id software and Blizzard

But with the change in demographics and casual gaming...I'd also throw Maxis into the ring as well.

EA offcourse. Their sports games have been a staple for over 20 years.

Capcom with Id Software and Blizzard taking a close second and third..

While Capcom didn't create many of the genres first, they are the ones who popularized these many genres.

Street Fighter 2, Final Fight, etc.

Devil May Cry which could be argued that it's not the first 3D action game to allow combos, but it is the first 3D action game where combos was a core element of the gameplay. Castlevania Lament of Innocence, Ninja Gaiden, God of War, Dante's Inferno, etc, used the gameplay style that made the series so popular, but God of War, and subsequently Dante's Inferno, went further than that by ripping off Devil Trigger under the name of Rage of the Gods.

Monster Hunter. Again, not the original quest type game, but it's led that type of genre into a new direction where there are a lot of ripoff style games. None of them very good, including Monster Hunter, but Japan loves them and some people over here. Ragnarok Odyssey, God Eater, Soul Sacrifice, etc.

As a developer that has such great ideas to actually push the industry forward, it's sad that this same developer gets caught up in doing nothing more than having constant rehashes of its games, even back in the day. While other developers copied them, Capcom had a ton of Final Fight, 1942, Street Fighter, etc, clones. This generation that's all we see of them. Milking their same franchises repeatedly. This gen they don't put out as many unique titles as they once did. What was once the biggest influence to the industry is now one of its worst detractors.