The fifth letter of the Roman alphabet, e is derived from the Greek letter epsilon which is much the same in appearance and function. The Semitic hê probably first represented a praying or calling human figure. In Semitic, the letter was pronounced /h/ (in foreign words also /e/), in Greek He became Εψιλον (Epsilon) with the value /e/. Etruscans and Romans followed this usage. Due to the Great Vowel Shift, English usage is rather different, namely /i:/ in ME or BEE, whereas other words like BED are quite close to Latin or Continental European usage.
Like other Latin vowels, e came in a long (sounded as in they) and a short variety (sounded as in pet). In other languages which use the letter it takes on various other values, sometimes with accents to indicate which one (ê,é,è,ë).
On computers the uppercase letter is represented with ASCII code 69 and the lowercase letter with code 101. This is the most common letter in English and many related languages, which has some implications in Cryptography.
E is a common abbreviation for the drug Ecstasy.