Original: Original Red Hot Chili Peppers members Hillel Slovak and Jack Irons left that band just prior to it receiving its first record contract, preferring to focus on What Is This?. Slovak rejoined the Chili Peppers for their second album and Irons for their third album.
Simplified: Hillel Slovak, Flea, and Jack Irons were members of both bands, but Slovak and Irons left after Red Hot Chili Peppers' first album.