A friend at Roland turned us on to these YouTube videos of Herbie Hancock and Chick Corea in early promotional films for the Polymoog synthesizer, which debuted in 1975. If the Sequential Prophet-5 gets credit for being the first portable, giggable polyphonic synth, that's because the Polymoog wasn't very commercially successful.
Serious gear geeks may notice that the instruments in the videos say "Polymoog Keyboard" on them. Wasn't that a later version that was more preset-based and had fewer controls? Yes, but originally, the Polymoog Synthesizer--which IS the one you see in the videos--was called the Polymoog Keyboard. Early in the shipping schedule, it was decided to change the name to incorporate "synthesizer," then the Polymoog Keyboard moniker resurfaced in 1978 on the preset version.
The most famous occurrence of the Polymoog sound is on Gary Numan's "Cars," which used the "Vox Humana" preset for those string-like lead sounds.
Enjoy Herbie and Chick raving about how cool it is to play chords on a synthesizer, and don't let little children watch the first video. Those goth mimes dancing around the Polymoog in the woods are a bit too scary ...
Part 1: Dave Luce explains the Polymoog
Part 2: Chick Corea and Herbie Hancock