The same Ashoka continued to slaughter en masse people who seemed to disagree with him, even after his conversion to Buddhism and taking up ahimsa (nonviolence) as a governing principle [1]. Except after his conversion he restricted the genocide to non-Buddhists. Though this may have been an improvement from before his conversion to Buddhism when he executed or enslaved the entire population of Kalinga [2].

[1] https://en.wikipedia.org/wiki/Ashokavadana

> Ashokavadana mentions two incidents of Ashoka turning towards violence after adopting Buddhism. In one instance, a non-Buddhist in Pundravardhana drew a picture showing the Buddha bowing at the feet of Nirgrantha Jnatiputra (identified with Mahavira, the founder of Jainism). On complaint from a Buddhist devotee, Ashoka issued an order to arrest him, and subsequently, another order to kill all the Ajivikas in Pundravardhana. Around 18,000 followers of the Ajivika sect were executed as a result of this order.

[2] https://en.wikipedia.org/wiki/Kalinga_War