Origin of the phrase: "Oh it's on"

I know there is a World of Warcraft quest with that as the title. I know there is the phrase “it’s on like Donkey Kong” but that seems to be an extension of “Oh it’s on” rather than the origin. My Google Fu has failed me on this one. Does anybody know, does it perhaps have no specific origin, or is it simply lost to the sands of time?

Lost in the mists of time, I would say. Probably originally from “it’s on the schedule” or somesuch, saying that something is on is pretty common. “Our camping trip is on for this weekend”, “Are we on for dinner tomorrow night?”, “He insulted her and the fight was on!”, etc., that last one being directly related to the meaning you asked about (IIUC).

At a minimum “it’s on” goes back to 1993 when there were two well-known rap songs by that title.

Or 1973 Marvin Gaye “Let’s get it on”

The earliest I recall seeing it was the South Park episode that parodied “You Got Served”.

I remember hearing “It’s on like a neckbone” from back in the 80s.

“It’s on!”, initially meaning a fight or other confrontation has started or is about to start, and later extended to other encounters, has been current in Australian slang since at least the early 1950s. There’s a well-known anti-war protest song from the early 1960s for which this phrase is the title.

I think the phrase mostly refers to expected events, or events about which there has been some tension or suspense. The circumstances are such that the protagonists and/or observers know there is likely to be a fight, a sexual encounter, or whatever, and they are simply waiting for someone to make the first move. When someone does, it’s on.

I would love to know what this means

And by the way that’s “It’s on like Donkey Kong and Robotron!”

Then there’s “it’s on like a marathon!”

Or, as a rather morbid friend has it, “it’s on like a stillborn!”

The story I’ve heard is that the “It’s on like Donkey Kong” originates from an arcade owner named Robert Mori in 1984. I’ve never heard that he said it with “Robotron”, although I guess it is possible. I’d be interested to see if you have any cite for that form of the phrase.

Naughty by Nature and Eazy-E both released songs called It’s On in 1993.