Raft had difficulty working with Bogart and refused to co-star with him. Eventually, Warner agreed to release Raft from his contract in 1943. After Raft had turned the role down, the studio gave Bogart the role of "Mad Dog" Roy Earle in the 1941 film "High Sierra", which helped establish him as a top star. Following "High Sierra" and after Raft had once again turned the part down, Bogart was given the leading role in John Huston's successful 1941 remake of the studio's 1931 pre-Code film, "The Maltese Falcon", based upon the Dashiell Hammett novel. Warner's cartoon unit had its roots in the independent Harman and Ising studio. From 1930 to 1933, Disney alumni Hugh Harman and Rudolf Ising produced musical cartoons for Leon Schlesinger, who sold them to Warner. Harman and Ising introduced their character Bosko in the first "Looney Tunes" cartoon, "Sinkin' in the Bathtub", and created a sister series, "Merrie Melodies", in 1931. Harman and Ising broke away from Schlesinger in 1933 due to a contractual dispute, taking Bosko with them to MGM. As a result, Schlesinger started his own studio, Leon Schlesinger Productions, which continued with "Merrie Melodies" while starting production on "Looney Tunes" starring Buddy, a Bosko clone. By the end of World War II, a new Schlesinger production team, including directors Friz Freleng (started in 1934), Tex Avery (started in 1935), Frank Tashlin (started in 1936), Bob Clampett (started in 1937), Chuck Jones (started in 1938), and Robert McKimson (started in 1946), was formed. Schlesinger's staff developed a fast-paced, irreverent style that made their cartoons globally popular. In 1935, Avery directed Porky Pig cartoons that established the character as the studio's first animated star. In addition to Porky, Daffy Duck (who debuted in 1937's "Porky's Duck Hunt"), Elmer Fudd ("Elmer's Candid Camera", 1940), Bugs Bunny ("A Wild Hare", 1940), and Tweety ("A Tale of Two Kitties", 1942) would achieve star power. By 1942, the Schlesinger studio had surpassed Walt Disney Studios as the most successful producer of animated shorts. Warner Bros. bought Schlesinger's cartoon unit in 1944 and renamed it Warner Bros. Cartoons.