Kommander wrote:
The personal pronoun I is capitalized to differentiate from the math symbol i.[citation needed]
Back when the Rules of Etiquette were established, it was considered socially unacceptable to refer to oneself as being a number or imaginary, rude to refer to oneself as the square root of anything, and extremely rude to refer to oneself as the square root of a negative number. Also, people were offended by math in general back then.

Speaking of numbers, I is number one, the way the Romans wrote it.