The GREEN GHOST that haunted the SEDGEWICK HOTEL was the first entity the GHOSTBUSTERS faced and trapped using their newly-developed equipment.
A dirty, destructive, and gluttonous class 5, the most fascinating thing about it is how it has translated into other dimensions.
Virtually everywhere else, it is a friendly mascot that can be trusted to roam freely around the firehouse; at the very least, it is not mean-spirited. (Pardon the pun.)
It's interesting to note that when the otherdimensional versions of the Green Ghost -- most of which have taken the name of "SLIMER" -- finally come face to face with the original, it reacts aggressively and frightens them.