Paul, or Jesus as his "friends" have taken to calling him, was first seen on top of a roof in the final page of issue #91 spying on the Alexandria community. His whereabouts were unknown until issue #92 where he met with Michonne and Abraham while they were on their routine perimeter check of the Alexandria Zone. After a brief confrontation with both of them, he demanded to meet with their leader, Rick. When things finally settled down a bit, Paul explained to Rick the reason for his arrival.
Much like Aaron used to do, one of Paul's tasks is to meet with new groups, establish connection, thus build a trade relationship between them. To Abraham's surprise, Paul revealed to them that there are more groups of survivors out there.
After Rick released Dwight, he assigned Paul to follow him. Once back at Negan's base, Paul is spotted by the others. After refusing to surrender, Paul is attacked by a woman named Tara who plans to kill him. Dwight however intervenes, telling her Paul is of more use to them alive.
It's also worth noting that Paul might be related to Spencer Monroe(as well as Douglas and Regina, even though they are dead now). They all share the same last name but nothing is certain yet.
Jesus was created by Robert Kirkman and Charlie Adlard. His first appearance was in Image's The Walking Dead #91.