In Marvel, the answer depends on whether the question is about the movies (MCU) or the main comics universe.

In the Marvel Cinematic Universe (MCU)

In the MCU, the Infinity Stones are not made by a person or race; they are formed when the universe itself begins. They are described as the remnants of six primordial “singularities” that existed before the Big Bang and were then compressed into Stones by cosmic entities as the universe came into being.

In Marvel Comics (Earth-616)

In the main comics continuity, the Infinity Gems originally come from a single, all‑powerful cosmic being called Nemesis, which destroyed itself because it could not bear to exist alone. The being’s essence then fragmented into the six (later seven) Infinity Gems, so in the comics the “creator” of the Gems is effectively Nemesis’ own self-destruction rather than an external forger.