As an actor, Anderson had to, at least abstractly, invent a backstory for his character, even though his past was left intentionally vague by the “John Wick: Chapter 4” filmmakers. His ideas weren’t written into the script, but they were a handy way to inform his character. Anderson took superficial elements of Mr. Nobody — his costume, his props, etc. — and reverse-engineered the “whys.” If Mr. Nobody had a mark on his body, it was Anderson’s job to invent the story as to how he got it. Those kinds of details clearly enriched his performance. Anderson said:
“I looked at the Joker and studied a lot of what Heath Ledger did, how exciting that character was; you just knew that guy had a robust past. Like, Why did he get those scars? And, for me, Why do I have this canine? Why do I have this knapsack? Why am I dressed like this? This guy’s transient. He has pockets because he travels so much; he doesn’t really change.”
It seems the only direct connection Mr. Nobody had with the Joker was that he was resolute, but also mysterious. Audiences could understand his standpoint and his motivation while never understanding his path or his backstory. It’s an effective way to keep viewers intrigued, while still allowing the character to be mutable and mysterious. The principle is the thing. Even if the principle is related to chaos and/or murder.