Saint Christopher is venerated by several Christian denominations as a martyr killed in the third or fourth century. However his veneration only appears late in Christian tradition, and did not become widespread in the Western Church until the Late Middle Ages, although churches and monasteries were named after him by the 7th century.
His most famous legend tells that he carried a child, who was unknown to him, across a river before the child revealed himself as Christ. Therefore, he is the patron saint of travellers, and small images of him are often worn around the neck, on a bracelet, carried in a pocket, or placed in vehicles by Christians.
Information from Wikipedia.