Sir Lewis Thomas Casson (26 October 1875 – 16 May 1969) was an English actor and theatre director, and the husband of actress Dame Sybil Thorndike.

In 1891 Casson's father decided to make a business of his hobby of building organs, and the family moved to London.

When this failed, he began studying chemistry, but then trained as a teacher at St Mark's College, Chelsea, where he gained a teaching certificate.

In 1900 Casson's father began another organ making business and Lewis worked in this for the next four years.

In 1909 Sybil gave birth to their first son, John, and soon after, they joined Frohman on a tour of the United States.

He then succeeded Alfred Wareing as the producer of the Scottish Playgoers Company, based in Glasgow, and forerunner of the Citizens' Theatre, in which his elder son John would become an actor-director.

[3] During World War II Casson organised tours of the Old Vic company to the South Wales valleys.

In 1959, Casson and Thorndike celebrated the golden jubilee of their wedding by appearing together in Clemence Dane's play, specially written for them, Eighty in the Shade.