self-constituted

adjective

self-con·​sti·​tut·​ed ˌself-ˈkän(t)-stə-ˌt(y)ü-təd 

: constituted or appointed by oneself to something (such as a function or position)

a self-constituted leader

But the old gentleman, his self-constituted companion, did not allow him to recede from the invitation …

—Sir Walter Scott

Word History

First Known Use

1657, in the meaning defined above