I am sure, everyone in this forum knows, that the Trimurti is One, but
how would Bhakti poetry have been possible without the separation of the three?
How could Arjuna receive a weapon from Shiva?
How could Krishna offer Arjuna to be his charioteer?
How could Rama broke Shiva's bow?
How could Ayyappan be born?
How could Shiva borrow Brahmas swan?
How could Shiva start dancing, crying for Gauranga?

Rig Veda I.164.46 - Viśvedevas
They call Him Indra, Mitra, Varuṇa, Agni, and He is heavenly nobly-winged Garutmān.
To what is One, sages give many a title they call it Agni, Yama, Mātariśvan.