All Indian mantric practices stem from the ancient Buddhists of India, and were adopted, with modifications, by the Shiva and Vaishanava sects as Hindu tantricism following the Gupta Age.
However, there are no bija mantras in the Rig Veda. According to what I've read, every bija mantra has four aspects: a rishi or seer, a raga or melody, a bija or seed sound, and a kilaka or pillar.
