Doc Minstrel was a minor character in the story Fallout: Equestria - Murky Number Seven.
He featured in Chapter 8: The Virtue of Freedom.
Doc Minstrel was a medically trained pony who originally came from a Stable. He was medically trained - at least well enough to treat Murky's injuries.
His presence was known to the slavers of Fillydelphia but he was not taken. He was on the payroll of Filly because he would turn over escaped slaves, and sell home-brewed alcohol and salvage from unexplored areas of Fillydelphia not yet controlled by Red Eye's forces.
He scavenges and trades in the Fillydelphia area in order save the bottlecaps to return to his wife; Chorale Sonata whom he loves dearly but has been separated from for a number of years. This drives him to betray Murky and turn him over to the slavers of Fillydephia.
Minstrel was killed by Protege as punishment for his betrayal to Murky which led to the enslaving of Sunny and the death of her loyal pet Cayenne.