Foster MacKenzie III (July 9, 1944 – June 8, 1993), known professionally as Root Boy Slim, was an American musician and songwriter.

He was an exceptionally bright child with parents who were able to afford a series of costly prep schools, and he attended Yale University.

In the 1970s, he formed his own alternative rock band (including musicians such as tenor saxophonist Ron Holloway) and an ensemble titled Crying Out Loud.

Mackenzie's group was ultimately billed as Root Boy Slim and the Sex Change Band and The Rootettes.

Band members wore ermine capes and silver lamé hot pants and boasted that they were never invited for return engagements.

[2] After graduation, MacKenzie drove an ice cream truck in Washington, D.C. One day he suffered a psychotic break after a particularly high dose of LSD, and he climbed over the White House fence.

Warner mismarketed the LP, and the band found themselves without a label—but not without having had a European tour, in which Root Boy became enamored with his forefathers' homeland: Scotland.

The film was produced and directed by Michael O'Donoghue, the famed Saturday Night Live head writer, and also featured appearances from Dan Aykroyd, Bill Murray, Laraine Newman, Gilda Radner, and Sid Vicious among others.

The ban was lifted in 1980, and Root Boy and crew triumphantly returned in a concert in the university's Ritchie Coliseum.

For nightclub performances, Root Boy was backed by a series of other bands, including Ron Holloway and Cryin' Out Loud, New Hope for the Criminally Insane, Capital Offense (featuring Wayne Tomlinson, Tommy Lepson, Timm Biery, Ron Holloway and Dominic Vigliotti), Barbecue Juiceheads, and the Humans.

By the time the fourth set began, there were at least 25 musicians on the stage who had recorded or played clubs with Root Boy during his career.

Slim's final resting place is in a grave beside his father's in Calvary Church Cemetery on Hendersonville Road in Fletcher, North Carolina, just south of Asheville.