To Paul the son of perdition is an AntiChrist figure who appears at the end of the world:
Let no man deceive you by any means: for that day [of Christ] shall not come, except there come a falling away first, and that man of sin be revealed, the son of perdition;
-- 2 Thessalonians 2:3
To John's Jesus the son of perdition is Judas, one of the Twelve, already come, and already lost, and completely uneschatological:
While I was with them in the world, I kept them in thy name: those that thou gavest me I have kept, and none of them is lost, but the son of perdition; that the scripture might be fulfilled.
-- John 17:12
