I don't know everything about Borus since it's Dorgus' backstory buuuut from what I do know
Most important figures are 1) Borus himself duh, and 2) Dorgus who was literally his first follower - Gyoin correct me if I am wrong on these accounts.
Most prominent preacher is again Dorgus
Started by Dorgus because his old god, Horus, betrayed him and he believed that Horus was evil and must have a twin who was good that would actually take care of us.
Or something along those lines.