His Prehistoric Past is a 1914 American short silent comedy film - Public Domain

His Prehistoric Past is a 1914 American short silent comedy film which is in the public domain and it's not eligible for copyright protection,

written and directed by Charlie Chaplin, featuring a Chaplin in a stone-age kingdom trying to usurp the crown of King Low-Brow to win the affections of the king's favorite wife. As this film was the final one that Chaplin made at Keystone Studios, it was also the last film he made with most of Keystone's regular roster of comedians. Co-star Mack Swain would not appear in another Chaplin movie until 1925 when he had a prominent role in the classic Chaplin feature film The Gold Rush.

How long are movies copyrighted?
All works published in the United States before 1923 are in the public domain. Works published after 1922, but before 1978 are protected for 95 years from the date of publication. If the work was created, but not published, before 1978, the copyright lasts for the life of the author plus 70 years.

What happens when a copyright expires?
After the period of copyright protection has expired, a work becomes available for use without permission from the copyright owner; it is said to be "in the public domain." Most works enter the public domain because their copyrights have expired.