Have you ever wondered why we write the word 'I' with a capital letter, but not 'he' or 'she' or 'we' or 'you'? (or 'me'?)
Historians think the reason is that the word 'I' in Old English was 'Ich' (as it still is in German today; one more proof that English is a Germanic language; so 'Welcome! You're one of us!')
Anyway, over time the English dropped off the 'ch' and were left with 'I'. This was such a short word, printers wanted to make sure that people saw it properly in books, so they made it into a capital.
Another secret of your native language brought to you by your you-know-who.