The title is subjective and depends on individual preferences and criteria. Some potential candidates often mentioned include:
* Led Zeppelin: Known for their heavy sound, innovative use of instruments, and powerful performances.
* Black Sabbath: Pioneered heavy metal and dark, mystical themes, influencing countless bands.
* Deep Purple: Known for their virtuosic musicianship and epic compositions.
* AC/DC: Renowned for their high-energy live shows and classic hard rock anthems.
* Aerosmith: Combined hard rock with blues and pop influences, achieving massive commercial success.
Ultimately, the "King of Hard Rock" is a matter of opinion. Different individuals will favor different artists based on their own tastes and criteria.