actionist
/ˈakʃ(ə)nɪst/ /ˈakʃənɪst/noun
1A person who believes in or advocates action; a person who takes action.
2 Art. Also with capital initial. An artist of the actionism movement; specifically (in later use) = Viennese Actionist.
Origin
Early 18th century (in an earlier sense). From action + -ist.