Hoopy the Hoop

In the first Portal, Hoopy the Hoop was a lone hoop that dropped and rolled over in-front of the player at the end of the game. While Valve had anticipated Hoopy the Hoop would become an, cake took that place and Hoopy the Hoop was forgotten.

Portal
Hoopy the Hoop rolls across the screen at the end of the game

Portal 2
Hoopy is known to appear in a few places within Portal 2. His earlier known appearance is in Her Chamber, where he lays slightly to the left of what could be described as GLaDOS' head; his second known appearance is underneath a floor panel in Test Chamber 2. He makes his third known appearence behind a desk in Test Chamber 6; this is the same den as referred to by the Final Transmission achievement.