According to the Wikipedia article about Dramatis Personae, Dramatis Personae began in plays and later moved into the other forms of literature. This led me to ask: When did Dramatis Personae first appear in a work of literature that was not a play?
The first edition of Clarissa, or, the History of a Young Lady (1748) by Samuel Richardson begins with:
A brief Account of the principal Characters throughout the Whole.
Miss Clarissa Harlowe, a young Lady of great Delicacy; Mistress of all the Accomplements, natural and acquired, that adorn the Sex; having the strictest Notions of filial Duty.
Robert Lovelace, Esq; a Man of Birth and Fortune: Haughty, vindictive, humourously vain; equally intrepid and indefatigable in the Pursuit of his Pleasures—Making his Addresses to Miss Clarissa Harlowe.
James Harlowe, Esq; the Father of Miss Clarissa, Miss Arabella, and Mr. James Harlowe: Despotic, absolute; and, when offended, not easily forgiving. […]
Samuel Richardson (1748). Clarissa, or, the History of a Young Lady, volume 1, p. ix. London: S. Richardson
This has longer character descriptions than a typical dramatis personae, but it is close, and Richardson’s next novel The History of Sir Charles Grandison (1754) is even closer:
Names of the Principal Persons.
George Selby, Esq;
John Greville, Esq;
Richard Fenwick, Esq;
Miss Harriet Byron.
Mrs. Shirley, her Grandmother by the Mother’s Side.
Mrs. Selby, Sister to Miss Byron’s Father, and Wife of Mr. Selby.
Samuel Richardson (1754). The History of Sir Charles Grandison, volume 1, p. viii. London: S. Richardson.
Later editions of Clarissa were revised to contain a list similar to that in Charles Grandison, for example the sixth edition (1768) has:
Names of the Principal Persons
Miss Clarissa Harlowe, A young Lady of great Beauty and Merit.
Robert Lovelace, Esq; Her Admirer.
James Harlowe, Esq; Father of Clarissa.
Mrs. Harlowe, His Lady.
Samuel Richardson (1768). Clarissa, or, the History of a Young Lady (sixth edition), volume 1, p. xii. London: J. and F. Rivington.