The letter "V" is derived from the same root as the letters "Y," "W," "U," and "F." They all come from the word waw, and thus the "V" was originally pronounced as a "W."
During the Middle Ages, the letter "V" was interchangeable with the letter "U." Later the two were differentiated by their placement in a word. When the letter came at the beginning of a word, a "V" was used; when it came within a word, a "U" was used.
In Ancient Rome, the same symbol--V--was used for both. This letter was also used to represent the number five because of the counting practice of notching a "V" to represent five.
In some Latin grammar texts, the letter "V" was called the "consonantal U," but it became an official letter in the late 1700s due largely to the advent of the printing press which required differentiation between "U" and "V."
In modern usage, a "V" is not used like most other consonants in that it does generally not double to make a short vowel sound (as in humming and putting vs. living).