Krishna created the caste system

The four castes were emanated by Me [Krishna], by the different distribution of qualities and actions; know Me to be the author of them. 4:13

The four castes that Krishna created are the Brâhmanas (the priestly caste), Kshattriyas (the military caste), Vaishyas (merchants and farmers) and Shûdras (lowest caste, workers and servants).

Of Brâhmanas, Kshattriyas, Vaishyas and Shûdras, O Parantapa, the duties have been distributed, according to the qualities born of their own natures. 18:41

The duties associated with the four castes are specified in 18:42-45

Duties of caste assigned at birth should not be abandoned.

Congenital duty, O son of Kunti, though defective, ought not to be abandoned. 18:48

When women become corrupt, the caste system breaks down, which drags people to hell.

Owing to predominance of lawlessness, O Krishna, the women of the family become corrupt; women corrupted, O Vârshneya, there ariseth caste confusion; This confusion draggeth to hell the slayers of the family. 1:41-42