Ruby first appeared when Rex first went to Crystal Island. Ruby played a very minor role in the episode.
In Crystal Island Adventure, Ruby was first seen joking around with Amethyst until Lapis told them to get back to work.
In A Trip to Crystal Island, Amethyst helped Philip by showing him what to do.
In The Second First Day, Ruby, along with Amethyst and Sapphire sleep at Knapford Sheds.
Ruby is a bit of a jokester. She likes goofing around instead of doing work. Ruby also is a bit short-tempered and known to hold a grudge.
Ruby is based on a hybrid of a GWR No. 1340 Trojan's shape and a GWR 1361 Class's bunker, with Hunslet underframes and valve gear, a smokebox protruding from her saddletank, external cylinders and motion, and sandboxes underneath the tanks on her footplate.
After her overhaul, she was given a 2-4-2 wheel arrangement.
Ruby is painted red with black lining. She has a black dome, and a red gemstone with a square facet. She also has the number 3 on her bunker in dark red.
She is slightly based on Ruby from Steven Universe.