A martyr.
That would depend on your religion.
A Krillin.
A Seismologist.
An atheist
Call the lender
It rather depends on your relation to the person, his religion, and his motives.If you are of the same religion and agree with his motives he might be a saint or martyr.If the person is an opposing religion he might be deluded, a fanatic or insaneif you are an atheist he would be deluded, mis lead, mistaken or potentially insane
If you're asking what you call someone who joins a religion, then you just still call them by their name. But if you're asking how you call someone who's joined a religion, calling them should still mostly be the same. Just dial the number on your phone, they're not going to kill you.
Dying for one's religion is often referred to as martyrdom.
Buy a new battery or call someone to jump your battery
They can be either Atheists or Agnostics.
We call those people "Hypocritical".
They are the De facto leader