As an English name, Caleb came into use after the Protestant Reformation. It was common among the Puritans, who introduced it to America in the 17th century.
As an English given name, Christopher has been in general use since the 15th century. It became very popular in the second half of the 20th century, reaching the top of the charts for England and Wales in the 1980s, and nearing it in the United States.
In Denmark this name was borne by three kings (their names are usually spelled Christoffer), including the 15th-century Christopher of Bavaria who also ruled Norway and Sweden. Other famous bearers include Italian explorer Christopher Columbus (1451-1506), English playwright Christopher Marlowe (1564-1593), English architect Christopher Wren (1632-1723) and the fictional character Christopher Robin from A. A. Milne's Winnie-the-Pooh books.
The name has been very common throughout the English-speaking world since end of the 20th century. In the United States it reached a high point in 2017, when it ranked as the fifth most popular name for boys.