U and V were once the same letter, split apart by medieval scribes
For centuries printers wrote upon as vpon and have as haue. U and V were a single letter with two shapes, pointed at the start of a word and rounded elsewhere, whatever sound it made. The French Academy did not fully accept them as separate letters until 1762.
The family tree starts in Egypt with a hieroglyph, probably of a mace or a bird, standing for a v or w sound. Phoenicians borrowed it as waw, and the Greeks split that into two letters: digamma for w, which eventually became our F, and upsilon for u. Latin took a stemless upsilon shaped like a modern V and used it both for the vowel and for the w sound, so via was pronounced roughly wia. Y, W and Cyrillic U are all relatives.
The two shapes began to part ways in the late Middle Ages. A Gothic alphabet dated 1386 is the first known to list U and V separately, placing V ahead. Printers still avoided a capital U in favour of V into the 17th century. The rounded form eventually became U and the pointed one V.
English asks a lot of the letter. It has short sounds, as in duck and put, and long ones, as in mule and rule, joins digraphs such as au and ou, becomes a w sound in quick and suave, and falls silent in unique and guard. It is the 13th most common letter in English words, about 2.8 percent. British spellings keep it in colour and labour where Americans drop it, and texting uses it for you.
Other languages give it different jobs. French u is a front rounded vowel, with ou used for the sound English speakers expect; Dutch spells that sound oe, and Welsh uses w. Beyond words, U is the chemical symbol for uranium, a symbol for potential energy in mechanics, and a rack-mounting unit of 44.50 millimetres for server equipment.
Source: U
