In the Bhagavad Purana, Vasudeva (Devanagari वसुदेव, IAST Vasudeva) was the father of the eighth incarnation of Vishnu, Krishna, and his siblings Balarama and Subhadra. He was a Yadav prince. He was the son of the Yadav king Shurasena. He was the brother of Nanda Baba, who took care of Krishna during his early years as a child. His other brother Devashrava is the actual father of Ekalavya who played a significant role in Mahabharata. His sister Kunti was married to Pandu. Kunti plays a big role later in the war Mahabharata.
Vasudeva is related to Bhagavatism that was largely formed by the 1st-millennium BCE where Vāsudeva (Krishna, the son of Vasudeva) was worshiped as supreme ultimate reality. This is evidenced by texts and archaeological evidence. As textual evidence, the Mahanarayana Upanishad records the verse:
We endeavor to know Narayana, we meditate on Vāsudeva and Vishnu bestows wisdom on us.
This verse asserts that Narayana, Vāsudeva (Krishna) and Vishnu are synonymous. The author and the century in which the above Mahanarayana Upanishad was composed is unknown. The relative chronology of the text, based on its poetic verse and textual style, has been proposed by Parmeshwaranand to the same period of composition as Katha, Isha, Mundaka and Shvetashvatara Upanishads, but before Maitri, Prashna and Mandukya Upanishad. Feuerstein places the relative composition chronology of Mahanarayana to be about that of Mundaka and Prashna Upanishads. These relative chronology estimates date the text to second half of 1st millennium BCE. Srinivasan suggests a later date for the composition of the Mahanarayana Upanishad, one after about 300 BCE and probably in the centuries around the start of the common era.
Other evidence is from archeological inscriptions, where Bhagavan is documented epigraphically to be from around 100 BCE, such as in the inscriptions of the Heliodorus pillar. An Indo-Greek ambassador from Taxila named Heliodorus, of this era, worked at the court of a Shunga king, and addresses himself as a Bhagavata on this pillar, an epithet scholars consider as evidence of Vāsudeva worship was well established in 1st millennium BCE. A popular short prayer for worhiping Vasudeva is Dwadashaakshar.