Pitch bend
The MIDI message that bends pitch continuously, and one of the few in 1.0 granted fourteen bits of resolution.
The message (status byte 0xE0) carries two data bytes that combine into 0–16383, with 8192 as rest. Most other controllers in MIDI 1.0 get only 128 steps, which would produce audible staircases in a pitch glide. How far the wheel bends isn't set by the message but by the receiver; the default is ±2 semitones, changed via RPN 0.
The wheel itself comes from the 1970 Minimoog, spring-loaded back to centre. Because the message applies to the whole channel it bends every note at once, which is precisely why MPE puts each note on a channel of its own.