Vi is a standard not a specific implementation. There was an original Vi, but since it's a standard unix tool, it got cloned by everyone who ever made a unix clone after it was added to BSD.

Vim can be invoked to conform to the vi standard, although usually it only gets used that way when a vim user is on an unfamiliar machine.

Interesting view. I've never seen vi as a standard. But it makes sense.

Technically something can't call itself Unix(tm) without vi(1) [0][1]

[0] http://pubs.opengroup.org/onlinepubs/7908799/xcu/vi.html [1] https://en.wikipedia.org/wiki/Single_UNIX_Specification

Well I made his short two word answer into an explanation.

I believe it was Stevie (a vi clone for the Atari ST).