1) Advocate 2) Advocator 3) Exponent 4) Proponent 
• (n.) One skilled un, or attached to, a ritual; one who advocates or practices ritualism.
Rit'u·al·ist noun [ CF. French ritualiste .] One skilled un, or attached to, a ritual; one who advocates or practices ritualism. 
[n] - an advocate of strict observance of ritualistic forms 2. [n] - a social anthropologist who is expert on rites and ceremonies
noun an advocate of strict observance of ritualistic forms