Lord Vishnu, the Supreme Self (Atma), is the source of everything, as explained in the Vedanta-sutra: janmady asya yatah. Because Brahma was born directly from Lord Vishnu, he is called Atma-yoni. He is also called Bhagavan, although generally, Bhagavan refers to the Supreme Personality of Godhead (Vishnu or Lord Krishna). Sometimes great personalities–such as demigods like Lord Brahma, Narada or Lord Shiva—are also addressed as Bhagavan because they carry out the purpose of the Supreme Personality of Godhead. Lord Brahma is called Bhagavan because he is the secondary creator of this universe. This designation, Bhagavan, is sometimes conferred upon a pure devotee by the grace of the Lord so that he will be very highly esteemed.
Source: A.C. Bhaktivedanta Swami Prabhupada (2014 edition), “Srimad Bhagavatam”, Fifth Canto, Chapter 05 – Text 07 & 39