Sources:

The rise and relevance today:

If you need the professional pitch correction features of Auto-Tune Artist, there are safe and even free alternatives available:

When a vocalist sings into a microphone, their voice is converted into an electrical signal and sent to a recording device. Auto-Tune software analyzes this signal and detects any pitch discrepancies. If the software detects a pitch error, it automatically adjusts the pitch to the nearest correct note.

Here's a write-up on Auto-Tune: