pro ‧ po ‧ nent /prəˈpəʊnənt $ -ˈpoʊ-/ BrE AmE noun [countable]
[ Date: 1500-1600 ; Language: Latin ; Origin: present participle of proponere ; ⇨ ↑ propound ]
someone who supports something or persuades people to do something SYN advocate ⇨ opponent
proponent of
Steinem has always been a strong proponent of women’s rights.
leading/main/major proponent
Dr George is one of the leading proponents of this view.