Very early stars were constructed out of material produced in the big bang. This would be almost totally hydrogen and helium with no "metals". It is easier to form more massive stars from such material as it is more transparent to radiation. Nevertheless, the largest of these "population III" stars are only mooted to be about 1000 solar masses.

Supermassive black holes need to grow (quickly), either by mergers or by rapid accretion of gas onto a much lower mass "seed" black hole.

Exactly how is a major unsolved astrophysics problem.

Very early stars were constructed out of material produced in the big bang. This would be almost totally hydrogen and helium with no "metals". It is easier to form more massive stars from such material as it is more transparent to radiation. Nevertheless, the largest of these population III stars are only mooted to be about 1000 solar masses.

Supermassive black holes therefore need to grow (quickly), either by mergers in clusters or between galaxies, or by rapid accretion of gas onto a much lower mass "seed" black hole.

Exactly how is a major unsolved astrophysics problem.