when I first started playing FO4 I was searching a train car and upon exiting I was one-shot by (if I remember correctly) what appeared to be a clown in a chefs hat. I think I was near Oberland Station at the time

anyone know who this NPC is and where I can locate him? I have revenge in mind

I found him walking down the tracks while following Dogmeat on Kellogs hunt. He had just finished killing a Deathclaw and had a shopping list on him. I bum rushed him and used my machete on him. I put his hat on my food and drink merchant at the Castle.

His name is Gruel and he killed me at Red Rocket. I got my revenge near Peabody House just south of Quincy Ruins.

Interesting. Do you know if there is a quest associated with the guy or is he just a wandering psycho?

Edit: This should probably be in spoilers section.

Man I was so hoping for an actual Clown...

Just a wandering psycho. From talking to friends who have been playing the game he seems to be a random encounter.