The Demolition-man is an alternate future that could possibly be The Person, it is unknown if this actually is the Person or not, or if he is just lying about his past, for all anyone knows, he could just be a nasty manipulative old man. The demolition-man fits into the Persons timeline at the end of his life, when he has turned corrupt & wanting more life than is available, he is hanging onto his life with everything he's got, and is willing too throw anything he's got to keep himself alive, even if it involves killing someone.
The Demolition-man was born/created at the end of Persons life (Apparently), He apparently is what Person will or can become if he makes a certain choice in his life, that choice has yet to be discovered as of yet, so his true origin remains unknown.
Meetings with The Person
The Demolition-man has encountered Person many times. They first encountered when the Demolition-man faked his Identity to get undercover, He tried to kill Person, but he was overthrown & sent into the corners of the universe. Their next meeting was 17th Persons Death row, Persons life was under threat, but strangely he was there to help, it was later revealed, that he was only in it apparently to save his own neck, because apparently, in his version of reality, 17th's death never happened. They later encountered at the Time-vents, where Person & him where thrown in, both escaped.
it is unknown if Demolition-man is against person just to kill him, or to prevent something bigger.