Ka is one of the names of Prajapati, a Vedic God. The
reference to the deity is found in the famous Hiranyagarphasukta (Rig Veda
X.121). Why Prajapati is known as Ka is mentioned in a story in the Aitareya
Brahmana by Acharya Sayana.
Prajapati is known as Ka because of his unexplainable
nature.
Some of the other explanations:
Ka is derived from root ‘kam’ which means to desire.
According to this derivation Prajapati is called ‘Ka’ because he has a constant
desire for creation.
Another derivation of Ka is from root ‘kam’ which means to
make happy. Prajapati is said to give happiness to all creatures.