There in the Treta Yuga were some fearful Danavas who were invincible in battle. They were known by the name of Kalkeyas and they possessed fearful prowess.
आसन् कृतयुगे घोरा दानवा युद्धदुर्मदाः। कालकेया इति ख्याता गणाः परमदारुणाः॥