Actor Edward Askew Sothern, ca. 1860s-1870s. (via)
On 15 October 1858, Our American Cousin premiered in New York. After a couple of unhappy weeks in the small role [of Lord Dundreary], Sothern began portraying the role as a lisping, skipping, eccentric, weak-minded fop prone to nonsensical references to sayings of his “bwother” Sam. His ad-libs were a sensation, earning good notices for his physical comedy and spawning much imitation and merry mockery on both sides of the Atlantic. His exaggerated, droopy side-whiskers became known as “Dundrearys”. Sothern gradually expanded the role, adding gags and business until it became the central figure of the play.
(via)