From Bulbapedia, the community-driven Pokémon encyclopedia.
Miles (Japanese: マイル Mile) is Skyla's grandfather and a former Gym Leader of the Mistralton Gym.
In the anime
Miles first appeared in Cilan Takes Flight! after Ash and his friends had just met Skyla. He retired from being the Gym Leader of Mistralton City in order to fulfill his dream of owning his own cargo business, with his granddaughter taking over Gym Leader duties for him. Like Ash and Cilan, he did not agree with Skyla's concept of using "Air Battles" to run the Gym. He then explained that she used to battle challengers the traditional way and was also very good, but battling them left her no time to fly her plane. As a result, she came up with the concept so she wouldn't waste her time. Although he disagreed with Skyla, he thought she might still have a point and thus gave up trying to convince her otherwise, only doing so again once Ash challenged Skyla to a proper battle himself.
Miles now serves as the Gym assistant for his granddaughter and refereed both Cilan and Ash's matches. Before Skyla battled Ash, she watched old videos of Miles battling challengers while he was the Gym Leader so she could pick up tips.
He reappeared in Climbing the Tower of Success!, where he hosted the Wishing Bell Festival. There, it was revealed that he is very knowledgeable of important female figures in Unova, mostly because he finds them attractive. Elesa is his favorite and even eliminated Cilan in the contest because his impression of her was not up to his standards.
In the games
It is mentioned that Skyla has a grandfather in the games as well but he was left nameless. It was said that he was once a great pilot.