Around the time Jesus was 30 years old, and before Jesus started his public ministry, John the Baptist appeared in the wilderness regions near Jerusalem. John warned people to stop their wrongdoing in preparation for Jesus` coming. John performed baptisms in the Jordan river. The baptisms were a ceremonial washing with water that represented a cleansing from wrongdoing and a commitment to do right. Jesus was baptized by John. As Jesus` ministry and popularity increased, John became less prominent. He was soon arrested by Herod and eventually beheaded.

To read more about John the Baptist see the following:

The account in Luke's Gospel

Again in Luke's Gospel here.

Read more here.

 And here.