There is no clear evidence of who was the first, but I believe it was Peter since Christ said he would build His Church on Peter.
Constatine
Clovis
Constantine the Great .
However, Constantine the Great didn't convert to Christianity until he was old and about to die.
At the end of the first Millennium - AD 988.
Constantine was the first emperor to convert to Christianity.
Clovis was the first important non-Roman king to convert to Christianity.
Trying to convert them into Christianity
The Cow
to convert many people to Christianity
chirst
Vladimir I ordered his subjects to convert to Orthodox Christianity.