In Pokémon Ruby, Sapphire, Omega Ruby, & Alpha Sapphire, Wallace is the Water-type Gym Leader of Sootopolis City. In Pokémon Emerald, he is instead the Champion of the Hoenn Region.
Alfred Russel Wallace was a British naturalist, explorer, geographer, anthropologist, biologist and illustrator. He is best known for independently conceiving the theory of evolution through natural selection; his paper on the subject was jointly published with some of Charles Darwin's writings in 1858.
Wallace Henry Hartley (June 2nd 1878 - April 15th 1912) was the band master on the RMS Titanic, and famously went down playing 'Nearer My God to Thee'.
Wallace Reid (b. April 15, 1891) was a silent film star and a famous bearer, though his birth name was William Wallace Reid. He was one of the most popular leading men of the 1910s and early 1920s, but after a 1919 accident he became addicted to morphine, leading to his early demise in 1923.
Wallace is one half of the dynamic duo, "Wallace and Gromit": a clamation series created by Aardman. Wallace is the wacky inventor who loves cheese, and Gromit is his practical and loyal dog. I felt the need to clarify from the above comment :)