Let's extract some in-game quotes...
"The Hero's triumph on Cataclysm's Eve
Wins three symbols of virtue.
The Master Sword he will then retrieve,
Keeping the Knight's line true."
From A Link to the Past. This is basically saying that the master sword is passed down the Hyrule knights to find its owner/hero. Also saying the three pendants are needed to get the sword. Anyone else find the same connection in other Zelda games? OoT - Three spiritual stones to get the master sword. Each stone/pendant is actual basing their power off the Goddesses, similar to the Triforce. So this hints at that the Goddesses had something to do with its origin.
"Suspecting that Ganon’s power was based on the Triforce’s magic, the people of Hyrule forged a sword resistant to magic which could repulse even powers granted by the Triforce."
From A link to the past. Nuff said.
"As the Seven Wise Men searched for a valiant person to take up the Master Sword, Ganon’s evil army swarmed from the tainted Golden Land into Hyrule and attacked the castle. The wise men and the Knights of Hyrule combined forces to wage war on this evil horde."
From A Link to the Past. Hinting that the sages (seven wise men) also had something to do withs its origin.
I may find quotes from OoT and other games later on. But simply put, its easy to figure out a "mystery" by actually paying attention to the game
So...it was either the people of Hyrule, the Goddesses or the Sages. And actually it was all three. The Sages were probably the "people of Hyrule" and used the power from the Gods to create the sword.