A son born of the womb of a Śūdra(Sudra) woman, and fathered by a Kṣatriya (Kshatriya) man is called Ugra. Such people are called Ugrakṣatriya in Vṛhaddharmapurāṇa (Vrihaddharmapurana). Perhaps they are the predecessors of the caste called Ugrakṣatriya.