In August 2014 Espressif (at that time an unknown Chinese company) released the ESP8266. It was meant to be used as a Wi-Fi bridge for other microcontrollers until someone noticed it had way more processing power and memory than those other microcontrollers.
Later that year in November, the SDK went public and a hacker (Ivan Grokhotkov, now working for Espressif) released a project to support the ESP8266 from within the Arduino IDE. And as they say in the books the rest is history.
Today Espressif makes 2 of the most famous silicon chips used in IOT eco-system, namely ESP32 and ESP8266. Here you can find various introduction, how-to and security related articles for these chips.