At the heart of the STM32 Blue Pill is an STM32 microcontroller from STMicroelectronics, specifically the STM32F103C8T6. This microcontroller is part of the Cortex-M3 family, known for its high performance, low power consumption, and advanced RISC architecture. The Blue Pill is compact, measuring just about 5.3 x 2.2 cm, yet it packs a punch with its robust set of features.