Indra became the great Indra only by slaying Vritra and obtained the lordship over the gods and the celestial cup for drinking wine and became the lord of the worlds.
इन्द्रो वृत्रवधेनैव महेन्द्रः समपद्यत। माहेन्द्रं च गृहं लेभे लोकानां चेश्वरोऽभवत्॥