By the late 1980s, Renaissance Technologies had found something rare — a system that worked. But what happened next was almost as unusual as the discovery itself.
In 1988, Jim Simons and mathematician James Ax launched Medallion, the fund that would eventually become the best-performing investment vehicle in modern financial history. Yet instead of opening it up to the world's wealthiest investors — the usual move for a fund posting extraordinary numbers — Renaissance did the opposite. Outside capital was slowly pushed out. By the mid-1990s, Medallion was almost entirely closed to outsiders, run overwhelmingly with the money of its own employees.
This wasn't modesty. It was strategy. Simons understood something most fund managers ignore: statistical edges decay as more money chases them. A model that works beautifully on a few hundred million dollars can break down entirely at several billion, because the very act of trading a strategy at scale erodes the mispricings it depends on. Rather than maximize assets under management — the way almost every other fund measured success — Renaissance capped Medallion's size and kept redirecting excess profits back to the people who built the models.
The result was a fund with no external investors to answer to, no pressure to explain quarterly performance to outsiders, and no incentive to grow beyond what the strategy could actually support. Just compounding, year after year, for the scientists inside the building.
In his own words: "We look for statistically significant anomalies... we don't need to know why they work, only that they do."
From 1988 to the early 2020s, Medallion is estimated to have returned north of 60% annually before fees — a figure that has no real peer in trading history. And almost no one outside Renaissance ever got to invest a single dollar in it.
Next: the secretive culture inside Renaissance — why almost nobody who joined ever left.