Frederick Warde - The Fools of Shakespeare: An Interpretation of Their Wit, Wisdom and Personalities (1913)
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A brisk look at Shakespeare's fools (in the plays six pretty clearly presented as such then Warde adds others who serve a similar function such as Hamlet's grave diggers). It starts with a quick historical overview of fools, so quick and from so few sources that it's not very reliable but does give an idea of what the actors were likely thinking. Then each chapter gets into the specific character with description of their parts and an analysis.
Frederick Warde (1851-1934) was a British actor with a special interest in Shakespeare who found more fame in the US performing around the country. One writer Alan Woods described him (in 1977) as "an old-fashioned, ranting performer". Warde claimed that at an 1875 performance of David Copperfield he was so overcome with emotion that he began sobbing and had to halt peforming. (Thomas P. Collins' Arizona on Stage p78) Warde was friends with the Barrymores and Douglas Fairbanks Jr (who made a point of meeting the older actor and gaining a small job that launched his career). Willa Cather saw him perform in Henry IV in 1891. He appeared in a few silent films including Richard III (1912) and King Lear (1916), the latter apparently using an optical dissolve to indicate the actor's transformation into Lear. He published a memoir Fifty Years of Make-Believe in 1920.