Most Knowledgeable About Kingdom Hearts

The First Kingdom Hearts game chronologically was an unknown title called "The Legend of Zelda"

A Hero named Link, traveled the lands when the worlds were still connected. With nothing but his sword, shield, and other gadgets, he wielded the master sword. A blade which could control Link's power.
You see, Link collected many hearts on his journey. Eventually gaining so many hearts in a specific timeline, that he managed to ascend beyond his mortal coil and become the entity known as kingdom Hearts. He did this so that even if he failed to beat Ganon and the worlds would separate, he could still keep them within his reach. His master sword eventually transformed into the X-Blade, and Ganon reincarnated years later as Xehanort (Yellow eyes)

When you begin Kingdom Hearts 1, you are given a choice to follow the path of the Warrior (Ganon) The path of the Mystic (Zelda) or the path of the Guardian (Link) as homage to Link's sacrifice and the tri-force.
These three would later be the inspiration for the drive forms of Valor, Wisdom, and Master.

Sora himself is thought of as "Wind Link" for his connection to people and destiny to be the one who will "Open the door."

It is often thought that Crash Bandicoot was the first kingdom hearts game, but this is a misconception. While it's true that Aku Aku and Uka Uka were the driving forces of Light and Darkness, it wasn't until the Tetris wars that they chose their champions.

From there it was "Ape Escape" onward to the 2002 release of the first Kingdom Hearts game.

 

While The Legend of Zelda is indeed one of the earliest games accredited to the Kingdom Hearts series, and not without good reason, many fans and critics are quick to overlook an even earlier predecessor in Color TV-Game 15--or, colloquially, Pong.

Unfortunately, the game has fallen into Canon Discontinuity of sorts with the series. While it does indeed depict the classic struggle between light and darkness bouncing the ball symbolic of the heart between them, with neither side truly emerging victorious over the other, despite occasionally gaining a temporary edge over the other, thus highlighting the precarious balance of the two forces, it is missing several...key elements added later in the series.

But then, there's another equally large camp insisting similarly that Color TV-Game 15 is actually not a Kingdom Hearts game, but instead the first Dissidia Final Fantasy game. Which, of course, is a completely ludicrous idea.