In the Krita age, O Partha, Krishna existed in the form of Virtuc. In the Treta age, he existed in the form of Knowledge. In the Dvapara age, he existed in the form of power. In the Kali age, he came to the Earth in the form of sin.
स्त्रेताकाले ज्ञानमनुप्रपन्नः। बलं त्वासीद् द्वापरे पार्थ कृष्णः कलौ त्वधर्म: क्षितिमेवाजगाम॥