Travis Leonard Blaylock (December 21, 1934 – June 16, 1984), better known as Harmonica Slim, was an American blues harmonicist, singer and songwriter. He had some commercial success in the 1950s; recordings of two songs he wrote, “Mary Helen” and “You Better Believe It” (both 1956), were modest hits. He released a total of six singles and toured alongside Percy Mayfield, Harmonica Fats, B.B. King, T-Bone Walker, Pee Wee Crayton and Ray Charles. His debut album was released in 1969. By the late 1970s, he had stopped playing the blues.

He is not to be confused with (as he has been in some sources) two other similarly named artists, James Isaac Moore (better known as Slim Harpo) and Richard Riley Riggins (1921–2003).

Blaylock was born in Texarkana, Texas. With encouragement from his neighbors, and by listening to records by Sonny Boy Williamson I, he became competent playing the harmonica by the age of twelve. He joined a gospel group, the Sunny South Gospel Singers, in the mid-1940s, and they performed on a local radio station, KCMC. In 1949, Harmonica Slim moved to Los Angeles, California, where he started to perform with several local blues groups. Through this work, gaining experience and local connections, he began playing in package shows including working part-time with the pianist Lloyd Glenn in Lowell Fulson‘s band.