This is designer Simon Koay's 'Superbet,' the alphabet with each letter represented by a particular superhero/supervillain. You can buy prints/mugs/phone cases etc. of the whole set or individual letters at his Society6 store HERE. Can you name them all? I only recognized about seven. Still, this is a great way to teach your little geek-child the alphabet. Alternatively, do what my parents did and tell them the alphabet isn't important because they were born to be a ditch-digger. 'The only thing you need to know is a shovel, back pain, and hand callouses,' my dad used to say.
Thanks to Angela W, whose name begins with a four if I'm not mistaken.