They are known as bronies (bro + pony)
My Little Pony originally started out as a plastic toy figure for girls almost 30 years ago, in 1983.
But the MLP that bronies like best is the animated series, especially "Friendship is Magic."
Here is a sample:
I find this entire concept confounding, but I do like that there are men who are able to break the strongest taboo in our culture - liking girl things.