He's one of the stars of the new Marvel movie Guardians of the Galaxy...
...but Groot was originally meant as a one-time "monster of the day" prevalent in Atlas Comics' sci-fi/fantasy books before they became Marvel in 1961!
Of course nobody (including writer Stan Lee) considered the super-termites might start eating the surrounding forest once they finished munching on Groot...
The cover-featured story from Tales to Astonish #13 (1960) was penciled by Jack Kirby and inked by Dick Ayers was Groot's only appearance (except for reprints) for 15 years until Incredible Hulk Annual #5 (1976) which combined an alien scientist's recreations of several pre-superhero-era monsters against The Hulk...
...including...
...as you'll see tomorrow.