Hugo Hasslo (16 May 1911 Bohuslän - 20 January 1994 Stockholm) was a Swedish operatic baritone. Hasslo studied in Stockholm with Hjaldis Ingebjart and Joseph Hislop and made his debut at the Stockholm Opera, as Guglielmo in Cosi fan tutte, in 1940, where he remained until 1964, quickly establishing himself as first baritone. In Stockholm, he took part in the creation of Natanael Berg's Genoveva, in 1947, and in Kurt Atterberg's Der Sturm, in 1948. He made guest appearances in Hamburg, the Royal Opera House in London, the Edinburgh Festival, the latters both in 1959.