Janos Prohaska was a Hungarian-born performer and costume maker who built and played several Original Series creatures, among them the Horta, the Mugato and the Excalbian Yarnek.
Janos Prohaska (1919–1974) specialised in playing animals and monsters in costumes of his own design, and was a familiar contributor to American television in the 1960s.
His Star Trek work began with The Cage, in which he played the ape-like and bird-like captives in the Talosian menagerie. For The Devil in the Dark he designed the Horta and crawled inside it himself; the story is often told that he demonstrated the costume for Gene Coon, who commissioned a script around it.
He returned as the horned white Mugato that bites Kirk in A Private Little War and as Yarnek, the rock creature who stages the contest between good and evil in The Savage Curtain. Prohaska died in an aircraft accident in 1974 while working on a documentary series.