The word "AllSpark" was coined by Robert N. Skir, story editor for Beast Machines Transformers. Bob Skir had a Beast Machines website with Questions and Answers about Beast Machines:
In the Beast Machines - Transformers Frequently Asked Questions (FAQ) section, the ninth page was written on July 21, 1999.
In it, a fan who had seen the sneak preview of the first episode at BotCon 99 asked the first question. Bob Skir provided the answer:
Q: There was reference to the matrix as being some sort of all-encompassing existence of energy that created life as we know it (the description kind of reminded me of "the force"). Is this the same physical matrix from G1 transformers that was housed inside the autobot leaders and can be opened to "light our darkest hour," or are we talking about something entirely different?
A: the answer is "A", The Force, God, the AllSpark.
Halfway down the page, another fan had a similar question about the Oracle.
Q: Is the Oracle a personification of Vector Sigma, a manifestation of Primus, or something different altogether?
A: It's the AllSpark, God, if you will. the spark of every transformer who has ever lived, or ever will live.
The fifteenth page had pretty much the same question about the Matrix:
Q: What exactly is the matrix? I've seen the movie and all the episodes of Beast Wars and Machines were they say something about the matrix, but i still cannot get it clear.
A: In Beast Machines, when we talk about the Matrix, we are talking about the AllSpark, made up of every Spark that ever was, and every Spark that ever will be. (Which, if you replace "Spark" with "Soul", is my definition of God.)
Note that the proper spelling of the word capitalizes the letters A and S, like this - AllSpark.
The AllSpark opened its doors on November 11, 1999, and has been in operation as an ezboard ever since that day.