Robert Porter McKimson Sr. (October 13, 1910 – September 29, 1977) was an American animator and illustrator, best known for his work on the Looney Tunes and Merrie Melodies series of cartoons from Warner Bros. Cartoons and later DePatie–Freleng Enterprises. He wrote and directed many animated cartoon shorts starring Bugs Bunny, Daffy Duck, Porky Pig, Foghorn Leghorn, Hippety Hopper, Speedy Gonzales, and the Tasmanian Devil, among other characters. He also developed Bugs Bunny's design in the 1943 short Tortoise Wins by a Hare.

After he was born in Denver, Colorado, on October 13, 1910, McKimson's family variously lived in Wray, Colorado, Los Angeles, and Canadian, Texas, before settling in Los Angeles in 1926. From 1927 to 1928, McKimson and his brother Tom illustrated a prospective children's book written by their mother titled Mouse Tales, the characters of which were notably similar to those of Walt Disney cartoons (e.g. Mickey Mouse). These drawings entered storage in the 1930s, resurfacing six decades later.

In mid-1929, Robert was offered a job at Walt Disney Studio as an assistant animator to Dick Lundy, while Tom apprenticed under Norm Ferguson. According to Tom, Disney animators attending Otis Art Institute with him recommended him, while Robert said they were hired after an aunt from Denver met Disney at a party. According to Robert, the studio included less than 30 people, comprising nine animators, each with one assistant. After three months, the brothers received a raise from $18 to $25. Despite little extant evidence, Lundy corroborated that the McKimsons worked for Disney.

In 1930, the brothers were offered a higher salary at an Altadena studio planned by Romer Grey, the oldest son of Western author Zane Grey. The Romer Grey Studio produced several cartoons, four featuring Binko the Bear Cub, developed by the McKimsons and bearing strong similarities to Mickey Mouse. Due to the Great Depression, Grey's studio was unable to close a distribution deal. No shorts were released, with only a handful completed (and only one known to survive).

At the same time he began working for Grey, McKimson was hired by Hugh Harman and Rudolf Ising, first doing ink-and-paint duties for the first Looney Tunes, then becoming an in-betweener before becoming an animator by 1931, when the Romer Grey Studio shut down. At that time he had an accident that gave him a concussion. As a result, he was able to visualize better, thus increasing his production and animation. He was the head animator and go-to guy in the late 1930s at the studio, which overwhelmed him. Eventually he worked exclusively with Bob Clampett. He was offered a directorial position by Leon Schlesinger in 1938, but declined, allowing the position to go to animator Chuck Jones. He eventually accepted his own directorial position in late 1944, when Frank Tashlin left Warner Bros. to direct live-action films.

McKimson's first Warner Bros. cartoon that he finished, The Return of Mr. Hook, was released in 1945 exclusively for the U.S. Navy. His first theatrical short, Daffy Doodles, was released in early April 1946. His third theatrical short entitled Acrobatty Bunny would be the first Bugs Bunny short McKimson directed. It was released in June 1946. His better-known efforts include Hillbilly Hare, A-Lad-In His Lamp, Stupor Duck, The Windblown Hare, Walky Talky Hawky, and Big Top Bunny.

McKimson created characters like Foghorn Leghorn and the Tasmanian Devil, as well as directing every Hippety Hopper/Sylvester pairing. He also created Speedy Gonzales for the 1953 short Cat-Tails for Two and directed many others periodically (along with Friz Freleng and other directors) for the remainder of his theatrical career.

In June 1953, the Warner Bros. cartoon studio was shut down for a period of six months due to the 3-D fad at the time, which Jack Warner found to be too costly a process to use for animated cartoons. McKimson's unit however was disbanded entirely two months before the shutdown. He would make an Oldsmobile commercial at Cascade Studios around this time.