tritagonist

[trih-tag-uh-nist] /trɪˈtæg ə nɪst/

noun

(in ancient Greece) the third member of an acting troupe, which always consisted of three actors.

Compare protagonist (def 4), deuteragonist.

Origin

1885-90; < Greek tritagōnistḗs, equivalent to trit(ós) third + agōnistḗs actor, competitor, agent derivative of agōnízesthai to contend, struggle, compete for the acting prize