Sludge

Sludge is a male dragon who appears as the antagonist of the season eight episode Father Knows Beast, pretending to be Spike's father. He is named Shale in some merchandise.

History
In Father Knows Beast, Sludge first appears falling out of the sky like a fireball and crash-landing in Ponyville near Spike and Smolder. Sludge suffers a broken arm and sprained wings as a result of his crash, so Spike takes him to the Castle of Friendship to recover. The Mane Six offer to let him stay until he gets back on his feet. Sludge is resistant to accept help from ponies at first, but he accepts, and they nurse him back to health.

Before departing from Ponyville, Sludge remarks how happy he is that Spike found such great friends and a home, and he reveals that he is Spike's father. He tells a story of how Spike was orphaned as an egg, and the two proceed to engage in several father/son activities together. When Sludge later comments how little like a dragon Spike is due to growing up among ponies, he—at Twilight Sparkle's suggestion—decides to show Spike how to be a real dragon. By the end, Sludge effectively takes over Spike's bedroom and gets Spike to do everything for him.

When Spike—at Smolder's suggestion—wants to move himself and Sludge to an uncomfortable cave so they can live like real dragons, a panicked Sludge confesses that he is not Spike's father and only pretended to be in order to live a life of castle luxury. Arguing that he simply did what any other dragon would have done in the same situation, Sludge takes his leave of Ponyville.