The distinguished (and recently Knighted) stage actor Sir Patrick Stewart (Caption Picard of the USS Enterprise) can be seen here in rehearsal as Shylock in The Merchant of Venice, and discussing the role here.
You can find vintage performance and documentary footage at Theatre in Video— for instance an interview with Sean O’Casey, or Meryl Streep in a full-length 1981 performance of Elizabeth Swados’ Alice at the Palace.