The first mu’azzin of Islam was Hazrat Bilaal (radhiyallahu ‘anhu). His position in Islam is unique and exclusive on account of him being the first mu’azzin of Islam and the mu’azzin of Rasulullah (sallallahu ‘alaihi wasallam).

عن عبد الله بن عمر قال : قال رسول الله صلى الله عليه و سلم ثلاثة على كثبان المسك أراه قال يوم القيامة يغبطهم الأولون والآخرون رجل ينادي بالصلوات الخمس في كل يوم وليلة ورجل يؤم قوما وهم به راضون وعبد أدى حق الله وحق مواليه (سنن الترمذي #2566)

Hazrat ‘Abdullah bin ‘Umar (radhiyallahu ‘anhuma) reports that Rasulullah (sallallahu ‘alaihi wasallam) said, “Three groups of people will be on mountains of musk (i.e. on the day of Qiyaamah), and the former and the latter people will envy their position. The first is that person who used to call out the azaan everyday for the five daily salaah. The second is that person who led the people in salaah while they were pleased with him (i.e. he fulfilled the obligation of salaah in its proper manner). The third is that slave who fulfilled the rights of Allah Ta’ala and the rights of his masters.”