"Molosser" is the name of a group of dog breeds probably all descended from the same stock way back when. They're all solidly built and usually pretty large. The mastiff and bully breeds are Molossers, but I'm pretty sure the Saint Bernard, Rottie, Bernese Mt Dog, and Dobe are too. There are a ton more. My boy has Shar Pei in him and they are Molossers, too!