I randomly made Stormglaze’s cutie mark a tornado, although that didn’t really seem to fit along with his personality.  
So I gave him a backstory.
 
He got his cutie mark for his ability to make tornadoes, necessary for bringing rainwater and such, and he was actually pretty good at it.  
But one day he got into an accident and lost control while in the middle of a twister. This resulted in…well this: http://usagi-zakura.tumblr.com/post/108944886187/so-i-redesigned-stormglaze-a-bit-i-figured-at and afterwards he was so traumatized he refused to go back to his job.  
So he was instead given the one job no one else wanted.  
A Royal Guard for the least popular alicorn in existence.