Gus, although not one of my favorites from Old Possum's Book of Practical Cats, is an interesting character nonetheless. After reading this summary, I would suggest watching the excerpt from the movie adaptation of Cats, or at least listening to the musical version of the song. It's worth it.
Gus could always be found at the theatre door. His name is really "Asparagus," but too many people couldn't pronounce that, so his nickname became "Gus." Gus is an old cat: shabby, thin, and shaky. He was supposedly quite a cat in his youth, though. The exploits of his old days are what Gus likes to talk about with his friends, especially his adaptation of "Firefrorefiddle, the Fiend of the Fell." He boasts of the roles he played in his prime. And if someone gives him a bit of gin, he'll go on and on about roles he doesn't usually speak of. He is "old school" theatre (as it were), and he doesn't trust these young lads that "do not get trained." He thinks that naught can compare to his greatest role (which he repeats many times) and admits that "Theatre's certainly not what it was."
"Gus: The Theatre Cat" is one of the selections in T.S. Eliot's Old Possum's Book of Practical Cats. He's an old cat who lives in the theatre and reminisces to all who will hear of the roles he has acted in over his life. Much of the poem consists of Gus recounting the acts he has performed.
Also Little Nell mentioned in the poem was most likely the character from Dickens "Old Curriosity Shop" whom all England wept for.
Also acted with Henry Irving http://en.wikipedia.org/wiki/Henry_Irving and Herbert Beerbohm Tree http://en.wikipedia.org/wiki/Herbert_Beerbohm_Tree. East Lynne mentioned in the poem was famous for melodrama's.