Brahma is one of the names of the almighty God. It is also a common name given to the men. It also used to be a title which was given to highly qualified Rishis.
The Omnipotent Being of Brahma through his manifested will, revealed the Vedic Knowledge to the four Rishis for the welfare of the mankind. Metaphysically, this is described as Brahma chanting the Vedas through his four mouths.
"After the revelation, the great soul called 'Paramesthi Brahma' learnt the Vedas from the four original teachers in order to extend its knowledge of the Universe and fulfill that objectives of creation." - Manu Smriti