ATmega32U4 TQFP

The ATMega32U4 is Atmel's low-power 8-bit AVR RISC-based microcontroller featuring 32KB self-programming flash program memory, 2.5KB SRAM, 1KB EEPROM, USB 2.0 full-speed/low speed device, 12-channel 10-bit A/D-converter, and JTAG interface for on-chip-debug.

This is the same controller that's used on the Pro Micro and Fio v3.