Duelbot

Duelbot is a robot boss summoned by the Mechanist in the Fallout 4 add-on Automatron. It is an assaultron armed with highly damaging melee weapons.

Background
Duelbot is one of the many robots built by the Mechanist, it is used as a last defense against intruders. The robot seems to be a modified assultron with a sword attached to one arm and covered in scrap metal plating.