The Dota Auto Chess mod kicked off at the beginning of 2019, and started a trend in the process.
After reaching an apex of eight million players over a scant few months, the "auto-battler" genre was born, and man did publishers rush to it like old prospectors. From there Auto Chess morphed into a full standalone game (on mobile now and later slated for the Epic Games Store), and spurred Valve into making it official with Dota Underlords. In turn Riot Games responded with Teamfight Tactics, and Tencent developed Chess Rush.
Yes, just like DOTA, this cottage industry all started with a mod. Here are a few of the biggest current games.