By the time the story reaches the Brahmanas and the Puranas it has acquired a moral problem that the Rigveda does not have.
The later versions give Vritra a maker and a motive. Tvashtr, the artificer, produces a three headed son whom Indra kills out of suspicion, and then creates Vritra from the sacrificial fire to avenge him. Vritra is made a brahmin, which turns the central heroic deed of the Vedic religion into the gravest offence its law knows, the killing of a brahmin. Indra's victory is followed by pursuit: he flees, hides in the stalk of a lotus, loses his throne to the usurper Nahusha, and is cleansed only when the sin is distributed in portions among the earth, the trees, women and the waters, each receiving a share and a compensating blemish.
Some versions go further still and make Vritra a devotee. In the telling given in the Bhagavata Purana he speaks at length before the final exchange, asking not for victory but for uninterrupted remembrance of the Lord, and dies in that state, so that the demon is the more admirable party in his own death scene.
The Avestan side of the inheritance took a different route. Verethragna, whose name is the same compound, is not a slayer of a particular dragon but a god of victory itself, appearing in ten forms including a wind, a bull, a boar and a bird of prey. The obstruction has dropped out of the name and left only the smashing of it.