BT21 (also known as UNIVERSTAR BT21) is a collaboration project between BTS and LINE FRIENDS. BT21 features a cast of 8 charactes drawn by BTS. Each character represents a member, and the eight represents ARMYs. BT21 has gained significant popularity, even having its own spinoff game and merch line.
Here's the characters that represent each member:
TATA is an alien who became curious about the universe and accidentally crashed on earth. TATA represents Kim Taehyung
RJ is a polite Alpaca. He always wears a parka because he gets cold easily. RJ represents Kim Seokjin
CHIMMY is a puppy who'll try anything and is passionate at everything he does. CHIMMY represents Park Jimin
COOKY is a pink but tough bunny with dreams of being strong. COOKY represents Jeon Jungkook