Which comes first, the supermassive black hole or the galaxy?

That's like the chicken and egg question. Without ever having the physical ability to go back in time and check, we are left to hypothesize, reasonably of course.

I reckon they formed simultaneously if you consider Population III stars members of primordial galaxies like ours. But first, we need to know how the first supermassive black holes formed in the first place. If it is true that supermassive black holes are formed by the collapse of gas and dust clouds that got past the limit for building stars, then they may have formed simultaneously as the same gas and dust clouds were forming Population III stars. However, the harder question arrives if supermassive black holes are formed by the coalescence of the black hole remnants left by the very massive Population III stars. Stars are stars after all and they are how we primarily categorize galaxies. After supermassive black holes are set in place, more and more gas clouds are attracted to them or it can be that they clumped together in the crowded early universe. The clumping can be caused by local gravitational wells or the shockwaves from dying Population III stars, hence the early universe is not as spacious as it is now. Of course, feeding supermassive black holes are not like active vacuums, the feeding itself released jets of material that triggered more and more starburst from the surrounding gas and dust clouds. Quasars for example is a prevalent evidence for supermassive black hole formation in the early universe. This may have led to the foundation of galactic bulges for spiral galaxies the spheroid cores for ellipticals and dwarf spheroids themselves. The disk followed later for spirals. In this scenario, the galaxy as a whole should follow later after the formation of their supermassive black holes. The only confusion is how about galaxies without SMBH? The Triangulum Galaxy or M33 is a notorious example and a strong argument against this one. However, SMBH ejection scenarios can also counter this confusion let alone the age of the universe.

This is just my opinion, however...

Clear skies!

I think the supermassive black holes came first. They formed out of the giant clumps of matter that was much more dense in the universe back then. When the supermassive black holes formed, their gravitational influence and rotation helped organise the remaining matter around them into galaxies we see today.

it quite is maximum probable from an quite massive start up ending it quite is life. I ignore what the boundaries are yet above a undeniable decrease starts off will become a black hollow. that's a certainty that maximum galaxies (That we've appeared at) have a black hollow in the centre in spite of the certainty that that's confusing to declare whether the galaxy could 'disintegrate' the severe density of stars and subsequently the vast gravitational pull from those stars could desire to be sufficient to hold to galaxy mutually. i wish this is responded your question.

The galaxy came first. Before the universe, the galaxies came. Then eventually, caused by stars, the black holes came.

The real answer is nobody knows. In fact we're not really sure how to make SMBH at all. The easiest way to make them is via mergers (you can't have a star anywhere near massive enough to do this) but the rate of galaxy mergers is too low. We still don't know why the mass of a galaxy is linked to it's SMBH. It's all still a mystery.

Really good question

the galaxy comes first... then a star gets old, dies and collapses into a blackhole.... because stars are clustered together so tightly, it starts swallowing up its neighbors and becomes supermassive