Krishna

As per our scriptures, 

One who seeks/obtains/possess knowledge is Brahmin 

One who fights for/protects their nation is Kshatriya

One who trades and brings revenue to the nation is Vysya 

One who offers his services/labour is Sudhra

I think Krishna is all of this

The one who has put most knowledge of the world in one speech/narration (Bhagavadgita), if he's not the Brahman, who else would be?

The one who built his kingdom amidst water to avoid frequent invasions for the good of his people, who better is a Kshatriya?

The one who traded with kingdoms/nations afar and within Bharata khanda/Jambu dweepa and made his kingdom prosperous, who else is a better Vysya?

The one who was a cattle boy once and loved his cattle and protected them, who would deny him as a Sudhra?

I think that's why people treat him as completeness (Sampoorna) and worship him as GOD.