Johnny Horne, played by Robert Davenport and Robert Bauer, is Benjamin Horne's mentally handicapped son. He was tutored by Laura Palmer. His reaction to her death was to repeatedly bang his head against his dollhouse. Particularly fond of Native American Ancestry his Indian headdress was removed only for Laura's funeral (albeit after much gentle coaxing by Dr Lawrence Jacoby).
Several details about Johnny are revealed by Lawrence Jacoby in the deleted scenes of the Twin Peaks Definite Gold Box Edition DVD boxset. Johnny is 27 years old "going on 6," his favorite story read to him by Laura Palmer is Peter Pan (explaining his obsession with Native Americans), and, most notably, his brain is actually normal yet he chooses to remain a child due to an early unknown trauma, which Jacoby has strong hopes of curing.