well, yes, birth name is Izuku Midoriya, but Katsuki Bakugo, (who he calls 'Kacchan') called him 'Deku' to make fun of him.
he read it was Dek-U
BUT, Izuku made it his hero name when Ochako Uraraka, said it could also mean something else, bcuz she read it as De-Ku
:3
a bit of knowlage from an anime nerd for ya!!