Downedest mother fucker
(noun) Tried and true, faithful-to-the-end; unwaveringly loyal to the core; your #1 ally when the shit goes down and your cause may very well be a lost one.
I was worried about John going to that part of town, but then I learned Nikki was with him. Nikki considers John a friend and is the downedest mother fucker I know. By me learning that I brushed my worries to the side. Nikki would watch out for John and put John's well being above his own .