This is the boss you get at the end of wave 10.
I recommend purchasing 2 machine guns on your loadout and it will make it a very easy fight.
Just keep your distance and pepper it with machinegun fire and jump over any shockwave attacks that it creates.
About 1 min later its defeated and you will get the achievement.
A full playthrough and a bit extra to cover the random events is below if anyone needs a visual reference.