Voder (an acronym for "Voice Operating DEmonstratoR) made its premiere at the 1939 World's Fair, just like Elektro. But unlike Elektro, which used a built-in record player with a pre-recorded voice of a guy imitating a robot, Voder synthesized the human voice with an array of vacuum tubes, operated by a hu-man via an extremely complex interface:
There's one oscillator (which could be raised and lowered in pitch to change between male and female voices) and a hissing sound from a gas discharge tube used to simulate human breath. These were the only two actual audio sources; the rest was filter controls for ten vowels and four consonants, a volume accent button, and a footpedal pitch-bender. Allegedly, it took about a year for an operator to get the hang of it, making voder more musical instrument than robot.
Voder and Elektro totally should've hooked up at the fair.
Wendy Carlos does some email Q&A about the Voder and the Vocoder here.
Barely related, but very cool: a collection of toy robot commercials through the years.