The creation of the
iroha uta (as it is called in Japanese), along with the
hiragana alphabet itself is generally credited to
Kukai, who also founded the
Shingon school of
buddhism in the early 9th century.
The poem's form (four sets of seven-and-five syllables) is called imayo and was most popular during the Heian period. Its content elegantly describes the basic ideas if buddhism, namely that our worldly existence is fleeting and meaningless (called mono no aware in Japan), and that one should instead strive to achieve transcendence.