The FOUUUUUUUUUUUUUUUUUUUUUNNDDERRR is a meme used by the Gumball Wikia whenever Rigby1219 is mentioned, since The... FOUUUUUUUUUUUUUUUUUUUUUUUUNNNDDER is Rigby1219. He's the godliest user next to Elebizzyboi, who's good! How can you not like him? Russ can confirm this. Ele agrees!
It it speculated that The... FOUUUUUUUUUUUUUUUUUUUUUUNNDDERRR is dead, but that remains a mystery.