There’s a bunch of different autonomous groups, with no one “founder.”
https://www.charitynavigator.org/ein/474143254
https://projects.propublica.org/nonprofits/organizations/474143254
No... There's a proper 501-C that exists. So yes, there is a founder. While a lot of the marches are not necessarily associated directly with the organization, a lot of the donations get pooled into the organization. They make plenty of money doing it too.
Edit: There's also orgs like...
Black Lives Matter Global Network Foundation
As well associated with people like Khan-Cullors (https://nypost.com/2021/04/10/inside-blm-co-founder-patrisse-khan-cullors-real-estate-buying-binge/)