Christianity is an active religion practiced widely around the world, with more followers than any other in the modern era. It comes from the same origins as Judaism and Islam. The primary difference that separates Christianity from these other religions is the belief that Jesus Christ, the son of the god Jehovah and the human woman Mary, was crucified for mankind's sins. By contrast, followers of Judaism do not believe that Jesus is the messiah, nor has a messiah been born, whereas Islam recognizes Jesus as a prophet, rather than a messiah.
Over the course of history, followers of Christianity have fragmented into different branches of faith defined at the highest level as being either Catholic or Protestant. Catholics are followers of the Catholic church and its doctrine; the Catholic Church is headquartered at the Vatican, a city-state within Italy where the pope, or head of the Catholic Church, resides. Protestants, while following the same basic teachings of the Holy Bible, do not follow Catholic doctrine and are thus not followers of the pope.
Christianity in games
As a major part of Western culture for more than 1500 years, Christianity shows up in games in many different ways. Games set in the real, or a partially fictionalized world may have overtly Christian characters. It often features prominently in historical simmy games. For example, in Sid Meier's Colonization converting native peoples to Christianity is a game mechanic, and in Crusader Kings the Pope is an important political entity that interacts with player controlled characters. Dark mythologies which draw on Christianity, such as the Dracula story and anything with demons, are part of the inspiration for games like Castlevania and Devil May Cry. There are also a few Japanese games, exemplified by the Shin Memami Tensai series, that include biblical characters alongside supernatural entities from many world religions. And, inevitably, there are educational games that aim to teach children about the religion.