The ruler of this world is a Johannine term for the devil (see 12.31; 14.30). Jesus interprets his death, not as defeat, but rather as a triumph over the ruler of this world. Whereas 12.31 speaks of his judgment and defeat as a future event, the present verse speaks of it as a fact already accomplished.

The passive expression has already been judged must be made active in some languages. If so, it may be necessary to introduce God as the agent, for example, “because God has already condemned the ruler of this world.” In this context, certainly, judged is to be understood in the sense of “judged against” or “condemned.”

Quoted with permission from Newman, Barclay M. and Nida, Eugene A. A Handbook on the Gospel of John. (UBS Handbook Series). New York: UBS, 1980. For this and other handbooks for translators see here .