Weisslogia "The White Dragon"

Weisslogia was a Dragon known as The White Dragon, and the foster father of Sting Eucliffe. He taught Sting how to use the Magic once fabled to be able to kill Dragons themselves: Dragon Slayer Magic. White Dragon Slayer Magic gave Sting the characteristics of Weisslogia himself.

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However, Weisslogia instructed Sting to kill him and bathe in his blood so that he could become a "true" Dragon Slayer.

(Source: Fairy Tail Wiki)