Contributors is the fourth core element. If someone other than the primary author (or editor) contributed to the source in a way that is relevant to your paper, you can identify that person by including this element.
Personal author(s) with editor(s):
Tynan, Kenneth. "The Kansas Farm Murders." The Critical Response to Truman Capote, edited by Joseph J. Waldmeir and John C. Waldmeir, Greenwood Press, 1999, pp. 129-34.
Personal author(s) with translator(s):
Kafka, Franz. The Metamorphosis. Translated by Stanley Corngold, 2013 ed., Modern Library, 1915.
Multiple relevant contributors:
"Something Nice Back Home." directed by Stephen Williams, performance by Matthew Fox , Bad Robot, 2008.