Bill and Ted must get an A on their history exam, or their band will not be. Rufus, a man from the future, lends them a time machine in order to gather historical figures from the past to use in their presentation.
Rufus never introduces himself to Bill or Ted. Future versions of themselves knew his name because previous future versions of themselves introduced Rufus to their past selves. Thus, Rufus' name in their minds represents an ontological paradox, or information from nowhere.