Sherlock
When one hears the name Sherlock, they might think of a selfish, cold, apathetic, uncaring, rude bastard who lives for the thrill of a case that keeps him sane and, most importantly, not bored.
If one thinks that, they are utterly wrong.
Because even asses like Sherlock can be the most selfless, kind, and caring man who literally gives up everything for his best friend.
His only best friend.
The one, single person in the world that will actually deal with Sherlock's craziness, his insensitive comments, and will even forgive him for lying to him and leaving him with such feelings of grief and loss felt with such ardor that saying sorry shouldn't have been enough.
John didn't care though. Sherlock was back and that was all that mattered.
Sherlock never expected to be anyone's best friend or best man. He didn't expect John to deal with him long enough to care for him as much as John does. He never expected John to stick around long enough for Sherlock to grow affectionate of the ex-soldier. He never expected John to be his downfall, his one fatal flaw.
Because that was what John was, Sherlock's fatal flaw. His Achilles' heel.
Sherlock will "die" to protect John and everybody else close to them. Even if it meant hurting John and leaving him in a world of hurt.
Sherlock wouldn't let himself die from Mary's bullet for he needs to survive to protect John. Just like his staged death, Sherlock cannot really die for leaving Earth means he will be leaving John in danger. Sherlock cannot stomach the thought of that.
Sherlock will do anything to ensure the safety of his best friend and the woman that means everything to John, even if it means becoming a murderer and living in exile.
Because if murdering a human computer ensures that John and Mary will be safe and fine, than that's good enough for him.
Now, when one hears the name Sherlock, they might think of a selfless, kind, sacrificing, caring man who never expected to be anybody's best man or to care about someone so much that he gives up everything for him.