Short answers, pulled from the story.
Richard Cromwell was the last Lord Protector of the Commonwealth of England, Scotland and Ireland, holding the title from September 1658 to May 1659. Since the Restoration, the title has not been used in this way again.
It declared that Oliver Cromwell 'shall be, and is hereby declared to be, Lord Protector of the Commonwealth of England, Scotland and Ireland...for his life.' This 1653 document was the republican constitution that created the office.
Richard, Duke of Gloucester, held the title 'Lord Protector of the Realm' from the 10th of May 1483 to the 26th of June 1483. He ruled during the nominal reign of Edward V before taking the throne himself as Richard III.
George, Prince of Wales, was styled 'His Royal Highness the Prince Regent' in 1811 instead of Lord Protector. The older title's republican associations, from its use during the Commonwealth, had made it distasteful.
The title appears in Mary Shelley's novel The Last Man, held by Lord Raymond and then Ryland; in the 1987 television series The New Statesman; in the 2008 film adaptation of Prince Caspian, held by the antagonist Miraz; and in the 2020 film Wolfwalkers.
James Hamilton, Duke of Châtellerault, held the title 'Governor and Protector of the Kingdom' as protector for Mary, Queen of Scots. He served from the 3rd of January 1543 to the 12th of April 1554.