When Queen Elizabeth II participates in a public event, everything is carefully planned, choreographed, and stage-managed. People working with the Queen need to rehearse, so they call in Ella Slack. She's the Queen's stand-in.
Although she doesn't look much like the Queen, Slack is about the same height (just two inches shorter). She's close enough that event managers can rehearse as though Slack is the Queen. In this video by Great Big Story, Slack describes her work.
-via Messy Nessy Chic