He is Groot
Many of the MCU’s most beloved characters are on the newer side, with some exceptions like Captain America and Black Widow. That said, others have been around longer than anyone could imagine. Take Groot from The Guardians of the Galaxy.
When this tree-like alien appeared on screen, he became an instant hit thanks to his catchphrase, “I am Groot.” Nevertheless, when Stan Lee, Jack Kirby, and Larry Lieber first introduced him on paper in 1960, he was a monster from Planet X bent on causing chaos and destruction.
