Sentence:  <WSD>Janus</WSD>, with his two heads, his mystery, his depiction as both laughing and serious, and the obvious parallel this forms with the masks of attic tragedy and comedy would make him a double of the two-headed man, the conjurer, and an associate of the trickster in folk comedy as well. 
Meaning of the word marked with <WSD> tags:  The god of doorways, gates and transitions, and of beginnings and endings, having two faces looking in opposite directions.