Explanation:

 The Gayatri mantra is a 6,000-year-old verse recited by millions of Hindus every day all over the world. This mantra – Rigveda Samhita 3.62.10 – was composed by sage Vishwamitra. He composed most of the poems in the third section of the Rigveda.

This verse is called the Gayatri mantra possibly because it is composed in the poetic meter called Gayatri.