RIRs are notorious as the bullies of a mixed flock.
There are a lot of docile breeds. Orps, Brahmas, Cochins, Jersey Giants and silkies are among them.
I call JGs gentle giants.
There are lots of other "nice" breeds though.
Here are 2 good breed selection charts with characteristics.
Keep in mind that there can be a bully individual of a docile breed and vice versa. They're kind of like humans. Some are mean, some aren't.
By reputation (and I can vouch for this having had all of these breeds except the Faverolles), the most docile and gentle standard breeds are (in no particular order) Australorps, Orpingtons, Cochins, Brahmas, Sussex, and Faverolles. Of these breeds, Australorps are the best layers (a Black Australorp holds the brown egg laying record with 364 eggs in 365 days) and Cochins are the poorest (but the best brooders and mothers). Orpingtons, Brahmas, Sussex, and Faverolles all lay at pretty much the same rate, although Brahma eggs tend to run slightly smaller than the others.