The most frequently used letter in the English language is e, which has 12.49% of the total. This is followed by t (9.28%) and a (8.4%)
Why these letters?The gold (e) and bronze (a) medals are perhaps predictable. Every standard English word has a vowel - only 'psst' appears in the OED and 'psst' would not be in most lists of standard words! It is more surprising to see 't' to be up there on the winners rostrum.
E is the champion in other languages, too. George Perec famously wrote a detective novel in French without an es (as it were) La Disparition (1969). This was then translated into English by Gilbert Adair as A Void.
More on this topic here.
English Language Teaching Pack - only £1.99