A roller for a roller door has a roller bearing surrounded by a roller on the outer circumference and into which a bearing pin is inserted on the inner circumference, which protrudes in the axial direction from the roller bearing. The bearing pin has an inner part of a harder material and a bearing sleeve made of a softer material, wherein the inner part is pressed or screwed into the bearing sleeve. A method for mounting a roller includes injection molding a bearing sleeve made of plastic, inserting and/or screwing an inner part into an inner ring of a roller bearing and the bearing sleeve, and fixing the inner part to the bearing sleeve in a force-locked manner, and applying a roller to an outer ring of the roller bearing.