A bowler in the sport of cricket is usually a player whose speciality is bowling. A bowler who is also a competent batsman is known as an all-rounder.
There are several types of bowlers and most teams will have a variety available in the team to take advantage of pitch or weather conditions or known weaknesses of the opposition.
A fast bowler is usually the mainstay of a team's attack. He will take a long run up before bowling each ball to build momentum and rhythm and can deliver the cricket ball at speeds up to 100mph.
A medium pace bowler bowls somewhat more slowly and will often have some other weapon in his bowling arsenal rather than relying on speed. This might take the form of being able to swing the ball in the air or disguise the speed or length of his delivery to fool the batsman. Some medium pacers are simply accurate; they can repeatedly deliver the ball to a place which forces the batsman to defend rather than scoring runs.
A spin bowler usually bowls quite slowly and puts tremendous spin on the ball causing it to bounce at an angle off the pitch, forcing the batsman to treat each ball carefully. Generally spin bowlers give up the most runs but they all have "tricks" that they use to fool the batsman and get him out (such as the arm ball, googly, flipper, topspinner or doosra). Spin bowling is very much about deceit rather than speed.
See also