Who is that masked man?

The other day it was really pretty outside. Trevor decided to mow the lawn. Hollister wanted to go outside with him, so I said, "Okay, just get your shoes on." A while later I went outside to check on both of them and as I round the corner to the house, this is what I see.I immediately turned around, walked in the house and grabbed my camera. This was too good to pass up.

I said, "who is that masked man?". He proceeds to take off his mask.... and say, "It's just me Mom, Hollister"