Rubin “Sharp” Nails:
 
Born in the Diamond Dogs pack of Splendid Valley, Rubin is the son of the Beta Male, Quartz Eyes.  
Like all Diamond Dogs, Rubin has undergone tests to see if he could be a sniffer, a tunnel digger … or just a helper in the notch of the gems.  
Fortunately for him, he became one of the tunnel diggers.
 
Right away, he demonstrated a great ability to dig, with its very sharp nails (hence the nickname Sharp), but was never called to work too hard.  
One day, wanting to prove to be a real Diamond Dog, went to dig for himself in one of the already existing tunnel, one of the main.  
Causing it to collapse into ruin.  
Rubin was saved by the skin of our teeth by his father but, unfortunately, the latter perished.  
Enraged, Rover exile him from the pack, sending him to wander in the Everfree Forest.
 
Fortunately, he found an abandoned cave on a nearby mountain .  
In a short time, he managed to organize a nice den.  
He even managed to repair a radio, almost always tuned to a station of the mystery, called “The Mystery Socety of Deflated Eyes” (or MSDE).  
Obviously, the loneliness is increasingly felt.
 
Fortunately, he met a new friend named Little Fang.
 
 
Little Fang:
 
Saved by Fluttershy during a stormy night of Nightmare Night, Little Fang is, in a sense, his “child”.  
Also because, had it not been for her, Twilight would have ended.
 
During a night hike in the Everfree Forest, Little Fang was attacked by bandits, who had seen the profit in the capture of the changeling.  
After being almost captured, Rubin was able to save him, making escape the bandits.
 
After having hosted in his den for the night, the two shook a strong friendship, discovering to have tastes in common, such as MSDE.