-ist

(Greek > Latin: a suffix; one who believes in; one who is engaged in; someone who does something)

revivalist
1. A promoter, organizer, or preacher of the Bible, at a religious revival meeting; especially, such a meeting for evangelical Christians.
2. Someone who wishes to revive customs, ideas, or institutions.
revolutionist
rhabdoidephilist (s) (noun), rhabdoidephilists (pl)
One who delights in oddly shaped twigs: Tommy always brought home some strangely-shaped branches and sticks which he put on the window ledge in his room. His mother said that he was a real rhabdoidephilist.
rhabdomantist
Someone who searches for underground water or minerals by using a dowsing rod.
rhapsodist
rheologist
rheumatist
rheumatologist
rhinologist
A specialist in rhinology.
rhizotomist
rigorist
1. Someone who is of strict or rigid principles or manners.

In general, a person who adheres to severity or purity in anything.

2. Characterized by strictness or severity in principles or practice; rigid; strict; exacting.
ritualist
robotophilist
A collector of remote control gear.
roentgenologist
Radiologist, a physician who uses x-rays or other sources of radiation for diagnosis and treatment.
rotuliphilist
A collector of baby rattles.