True Blue was an old trustworthy horse belonging to Frit, aka the Bottle Man. Blue pulled Frit's wagon as he travelled from village to village all over Etheria collecting bottles to use in building his giant Monument to Freedom.
The two of them lived together in a small hovel on Frit's Mountain, where for years, none but the two of them set foot. However, one day members of the Evil Horde confiscated True Blue and set him to work on a treadmill in one of the villages. She-Ra rescued Blue and asked Kowl to stat with him as Blue knew the way home while She-Ra and her own steed, Swift Wind went ahead.
By the time Kowl and Blue arrived at the mountain, the Hordesmen had been driven off and Madame Razz had made sure Frit's monument could never be destroyed or even damaged again, having used a spell to turn the glass bottles into unbreakable. Viridean Crystal.