Founder of the Dominicans. This was the order that was responsible for the Inquisition — the mission to convert heretics in no uncertain fashion. If they wouldn’t join after a bit of mutilation then burn them.
DOMINIC was not himself responsible for this sort of thing — it was not put into practice until 1231.
He was more concerned with sorting out calendar reform so that the right dates to celebrate Easter could be known. So he is now the Patron of Astronomers.