Final answer:
Christian Slater appears as himself in the Sabre orientation video in Season 6, Episode 14 of 'The Office'.
Step-by-step explanation:
In Season 6, Episode 14 ("Sabre") of the U.S. television series The Office, the famous actor featured as himself in the Sabre orientation video is Christian Slater. This episode showcases the introduction of Sabre, the new parent company of Dunder Mifflin, and their efforts to integrate with the Scranton branch. Accordingly, Slater appears in the in-universe video to provide both comedic effect and to lend a sense of familiarity and importance to the corporate messaging delivered to employees of Dunder Mifflin.