Biography
Born in Ireland. In 1762 an army officer, later an Irish MP, playwright and author. He also became a part of the group surrounding Dr. Johnson, David Garrick, Edmund Burke, etc. Among his plays were the tragedies Braganza (1775), The Law of Lombardy (ca. 1779), The Count of Narbonne (1781) and Julia: Or, the Italian Lover (1787). Most of his plays were performed at Drury Lane.
Life with Boswell
Boswell apparently first met Jephson at Thomas Sheridan's home in London on December 31, 1762, praising his parodies highly.
Literature
Most of Jephson's play are available via the AbeBooks used books search engine. Search either for Robert Jephson or for the exact titles.