Catholics believe that the one true priest is Jesus Christ, but that in His earthly life, Jesus gave a share in his priesthood to the 12 apostles. The apostles in turn ordained other men to share in the priesthood of Christ (2 Timothy 1:6), and the priesthood has thus been handed on through the authority of the Church for two millennia.
The priesthood is not a position of power, but of service (Matthew 20:25-28, John 13:2-20).