Thunder Streak is a unicorn pony who appreciates Luna's night.
Thunder Streak was a unicorn pony with great talent but no one seemed to accept Luna's nighttime seriously like he did and often mocked him about it by calling him a "Night Lover".
Thunder Streak eventually had enough of being mocked about his love for Luna's night and refused for Luna to lower the moon one faithful day. Luna and Celestia tried to reason with Thunder Streak, but he wouldn't listen, resulting in his bitterness getting the better of him and turning him into Thunderwing, Unicron's most powerful follower. He vowed to make Luna's night last for eternity and all who denied it would plunge into chaos. Celestia and Luna relunctantly used the Elements of Harmony to defeat their enemy and imprisoned him in the moon forever. But little did they know that he was to return a thousand years after his banishment.
Returning to Equestria
He later returned as Thunderwing to finish what he started years back. He returned during the Summer Sun Celebration and announced his plot to make Luna's night last for eternity and all of Equestria would plunge into chaos at the same time.
Defeat and Reformation
He tried to stop the Elements from being used but he was foiled and was defeated and turned back into Thunder Streak. When Princess Luna and Celestia returned and confronted Thunder Streak, they asked him if he would put the past behind him and accept their friendship. He does and they reunite after years of separation. A celebration is held in Ponyville and Thunder Streak is forgiven by its citizens for his actions as Thunderwing.
Thunder Streak made his return to Ponyville to replenish his friendship with its citizens on Nightmare Night but the citizens still believed him to be Thunderwing and kept running away from him screaming. Twilight, Optimus, and Princess Luna went to talk to him in the Everfree Forest and found him sitting in front of the Thunderwing statue and nudging a piece of candy towards it.
Princess Twilight Sparkle's Summer Sun Celebration
Thunder Streak is a blue unicorn with a lightning bolt cutie mark.
He is a bit like Princess Luna, as he was the only pony who appreciated Luna's night.