My understanding is that we're not totally certain if all black holes form from stellar mass black holes.
There is a theory that black holes can form from direct collapse. In this case, as I understand it, it can skip the star phase and just collapse straight into a black hole.... but I really am not an expert.
And I HIGHLY recommend the PBS NOVA episode "Black Hole Apocalypse" (Jan 10, 2018, Season 45 Episode 1). It was on Netflix for a while (and may still be.)
There is a theory that black holes can form from direct collapse. In this case, as I understand it, it can skip the star phase and just collapse straight into a black hole.... but I really am not an expert.
You can find more here: https://en.wikipedia.org/wiki/Direct_collapse_black_hole
And I HIGHLY recommend the PBS NOVA episode "Black Hole Apocalypse" (Jan 10, 2018, Season 45 Episode 1). It was on Netflix for a while (and may still be.)
Edit: here is the full episode on PBS (thank you NOVA!!!) https://www.pbs.org/video/black-hole-apocalypse-yj34qi/