Ajātashatru (ruled 491-461 BCE) was a king of the Magadha empire that ruled north India.
There is not a great deal known about Ajatashatru. What is known is that he became a King of Magadha and the adjoining areas by murdering his father, Seniya/Bimbisara. Also, he was a contemporary of Buddha, was a patron of the then-new religion of Buddhism, and he let the Sangha function in his Kingdom.
Some details of his life are given in the earliest Buddhist scriptures of the Pali Canon. In the Samaññaphala Sutta, Buddha said that if Ajatasattu hadn't killed his father, he would have attained sotapannahood, a degree of enlightenment. But because he had killed his father he could not attain it.
According to Romila Thapar, Ajatashatru was responsible for building Pataliputra and strengthening the defences of the Magadhan capital, Rajagriha. The same historian reports that Ajatashatru murdered his father and predecessor Bimbisara in order to accede to the throne. This is also recorded in the Buddhist scripture, the Contemplation Sutra. Next, Ajatashatru, undertook the annexation of the kingdoms of Kosala and Kashi, and pursued a sixteen-year war against the Vriji confederacy of what is today north Bihar and Nepal. Legends say that the one who masterminded Ajatashatru's usurping of the throne was the schismatic monk Devadatta, the reasons being that Ajatashatru was said to have been convinced by Devadatta to help fund his schismatic sangha.