I want to find some informations and share what I might found about Krieg’s back story.
At first here are a lot of his line that might be relevant, I found them on the [wikia]:
- Where is she? Is she still alive? Did she get away?
- (If you ever kill an innocent person, I will destroy us.) Shut UP!!
(No. That’s the deal. You can kill as many of the deserving as you like, but the second your axe touches the flesh of an innocent, I’ll end this. All of it. A razor to the veins, just like that fugitive we tried to grab on Hera, remember?) Nnnnngh, get out of my head!! (…I’ll take that as a ‘yes.’)
While Raving Retribution is active:
- I’ll never forget the way her holes cried… The way she screamed in
agony as she pushed the knife slowly into my sternum… Such a
beautiful symphony of feelings, and at the end of it, she was so much
greater! My operatic diva of flesh and steel!!
- You’re gonna scream, just like she did; open mouth, open heart, blood
and noise forever piercing my skull, poisoning me with its
psychopathic purple liquid. We watched it all, and felt the knife
edge split down the middle… CAN YOU HEAR ME?!
- I can’t see her anymore… She was so clear and bright… but the
blood is in my eyes, and now I can only watch the ocean of
blood…Its waves crash against my forehead again and again, AND I
JUST NEED TO LEARN HOW TO SURF!!
- This is my favorite song! Dance to the drum beat of the ballistic,
fetishistic, sadistic piss-stick! Let the bullets scrape me clean and
never, ever, ever flash a sassy eye at the good doctor!
when finding his Assassin:
HE WAS THERE FOR THE BIRTHING! HE BROUGHT THEM INTO THE METAL FUN PALACE SO SHE COULD START THE PARTY!
Krieg is saying “she” like there were only one person he could mean, but sometimes she inflicts pain on him and in other scenarios she receives pain from someone. That seems confusing, but if we consider the [conversations] between doctor Samuels and Jack, it seems plausible that Jack makes doctor Samuels a test subject for having sympathy for the test subject and questioning him:
Handsome Jack: “Okie-dokie, Sammy, let’s say we start that test?”
Doctor Samuels: “It’s ‘Doctor Samuels’. The test subject is still conscious. You can’t expect me to–”
Handsome Jack: “Sorry baby. I can’t hear you over the sound of people not being injected with Eridium right now. This Vault Key didn’t make Eridium come outta the ground for nothing right? So, we’ve got it - might as well do some good with it! You’re not eager to be on the other side of that glass, are you sweetheart?”
Doctor Samuels: “…Commencing Eridium mutation test on subject number two. Subject: Erik Franks.”
Doctor Samuels: “Don’t call me --This subject is… unsuitable for testing. His husband has the Shivers. He could have transmitted–”
Handsome Jack: “Hey, remember that wife of yours? And how you wanted to see her, like, ever again?”
It makes perfect sense that doctor Samuels is “she”. It also explains the message Krieg got from Sir Hammerlock:
SALUTATIONS PSYCHO MAN I’M SORRY AS A SLICE WOUND SINCERELY SAMMY.
My theory is that doctor Samuels injected him with slag and did other things to him while still showing mercy. Then she was turned into a test subject, she and Krieg became Psycho-friends and were separate when they tried to escape.
Other lines from Krieg reveal that he thinks Pain is friendship/love, that explains why he still likes her even though she inflected pain on him. Doctor Samuels never wanted to perform experiments on conscious test subjects, she has empathy, but because this otherwise friendly person had to torture him Krieg’s mind established a connect between pain with friendship.
- Hurt the one you love! Do it!
- Friendship is pain.
- Shoot me 'til you love me!
- Friendship is hate!
When Moxxi asked him if he is had someone in his life he replied:
“THE TINY ONE AND THE SAD-FACED MOTHER AND THE BLUE TATTOO FOREVER AND EVER!”
I am guess that the TINY ONE is Tiny Tina, the BlUE TATTOO is probably Maya since he notes her blue tattoos when he sees her for the first time.