Early Buddhist analysis names three roots of unwholesome action, the akusala mula, and this is the first of them: craving toward whatever is pleasant, called lobha in the Pali Abhidhamma and raga in the Sanskrit and Tibetan traditions that built on it. The Dhammapada returns to the image constantly, warning that the craving of a heedless man spreads like a creeping vine, and the early suttas, the Majjhima Nikaya foremost among them, treat it as the engine of continued rebirth: what is grasped in craving is carried forward as becoming.
Buddhaghosa's Visuddhimagga, the fifth century systematisation of the path, keeps raga in its analysis of temperament, holding that a person of greedy disposition needs contemplation of the body's impermanence and unattractiveness as the specific antidote, not a general moral exhortation aimed at every practitioner alike.
Vasubandhu's Abhidharma widens the term further, making raga one of a longer taxonomy of afflictions, klesha, that obscure right seeing rather than a single named vice standing alone. The three poison list survives inside that wider taxonomy as its practical summary, the version most Buddhists actually learn, and this entry keeps to raga as the first and, by most tellings, most persistent of the three, the one whose subtler forms attach even to the practice meant to remove it.