皇
コウ, オウ, おうじ, おお, み
emperor
JLPT1 G6 S9 F721
As per 王# (extend) + an abbreviated form of 自 (original/originally) → originator of a ruling dynasty, one that extends from earth to heaven → *emperor*. Here, 王 also lends the specific notion "ruler".
[Full Kanji Etymology List]