A wisdom king (Sanskrit: विद्याराज; IAST: vidyārāja, Chinese: 明王; pinyin: Míngwáng; Japanese pronunciation: Myōō) is a type of wrathful deity in East Asian Buddhism.

Whereas the Sanskrit name is translated literally as "wisdom / knowledge king(s)," the term vidyā in Vajrayana Buddhism is also specifically used to denote mantras; the term may thus also be rendered "mantra king(s)." Vidyā is translated in Chinese with the character 明 (lit. "bright, radiant", figuratively "knowledge(able), wisdom, wise"), leading to a wide array of alternative translations such as "bright king(s)" or "radiant king(s)". A similar category of fierce deities known as herukas are found in Tibetan Buddhism.

The female counterparts of wisdom kings are known as wisdom queens (Sanskrit (IAST): vidyārājñī, Chinese and Japanese: 明妃; pinyin: Míngfēi; rōmaji: Myōhi).

Vidyārājas, as their name suggests, are originally conceived of as the guardians and personifications of esoteric wisdom (vidyā), namely mantras and dharanis. They were seen as embodying the mystic power contained in these sacred utterances.

During the early stages of esoteric (Vajrayana) Buddhism, many of the deities that would become known as vidyārājas (a term that only came into use around the late 7th-early 8th century) were mainly seen as attendants of bodhisattvas who were invoked for specific ends such as the removal of misfortune and obstacles to enlightenment. They personified certain attributes of these bodhisattvas such as their wisdom or the power of their voices and were held to perform various tasks such as gathering together sentient beings to whom the bodhisattva preaches, subjugating unruly elements, or protecting adherents of Buddhism. Eventually, these divinities became objects of veneration in their own right; no longer necessarily paired with a bodhisattva, they became considered as the manifestations of the bodhisattvas themselves and/or of buddhas, who are believed to assume terrifying forms as a means to save sentient beings out of compassion for them. A belief prevalent in the Japanese tradition known as the sanrinjin (三輪身, "bodies of the three wheels") theory for instance posits that five Wisdom Kings are the fierce incarnations (教令輪身, kyōryōrin-shin, lit. "embodiments of the wheel of injunction") of the Five Wisdom Buddhas, who appear both as gentle bodhisattvas who teach the Dharma through compassion and as terrifying vidyārājas who teach through fear, shocking nonbelievers into faith.

The evolution of the vidyārāja will be illustrated here by the deity Yamāntaka, one of the earliest Buddhist wrathful deities. In the 6th century text Mañjuśrī-mūla-kalpa, Yamāntaka is portrayed as the oath-bound servant of the bodhisattva Mañjuśrī who assembles all beings from across the world to hear the Buddha's preaching and vanquishes (and converts) those who are hostile to Buddhism; at the same time, Yamāntaka is also the personification of Mañjuśrī's dharani, the benefits of which are identical to his abilities. He was also commonly depicted in statuary along with Mañjuśrī as a diminutive yaksha-like attendant figure.

Later, as Yamāntaka and similar subordinates of various bodhisattvas (e.g. Hayagrīva, who was associated with Avalokiteśvara) became fully independent deities, they began to be portrayed by themselves and increasingly acquired iconographic attributes specific to each. Yamāntaka, for instance, is commonly shown with six heads, arms, and legs and riding or standing on a buffalo mount. The status and function of these deities have shifted from being minor emissaries who gather together and intimidate recalcitrant beings to being intimately involved in the primary task of esoteric Buddhism: the transformation of passions and ignorance (avidyā) into compassion and wisdom. As a result of this development, the relationship between Mañjuśrī and Yamāntaka was recontextualized such that Yamāntaka is now considered to be the incarnation of Mañjuśrī himself (so the Mañjuśrī-nāma-samgīti). Eventually, in the sanrinjin interpretation of Japanese esoteric Buddhism, both Yamāntaka and Mañjuśrī - under the name Vajratīkṣṇa (金剛利菩薩, Kongōri Bosatsu) - became classified as avatars of the buddha Amitābha.

Other Wisdom Kings followed a more or less similar development. Hayagrīva, for example, was originally the horse-headed incarnation of the Hindu god Vishnu which was adopted into Buddhism as Avalokiteśvara's attendant (although unlike the Hindu Hayagrīva, the Buddhist figure was never portrayed with a horse's head, instead being depicted like Yamāntaka as a yaksha who may have a miniature horse head emerging from his hair). Eventually, as Hayagrīva increasingly rose to prominence, the distinction between him and his superior became increasingly blurred so that he ultimately turned into one of Avalokiteśvara's many guises in both China and Japan. One of the more famous vidyārājas, Acala (Acalanātha), was originally an acolyte or messenger of the buddha Vairocana before he was interpreted as Vairocana's fierce aspect or kyōryōrin-shin in the Japanese tradition. (In Nepal and Tibet, meanwhile, he is instead identified as the incarnation of either Mañjuśrī or the buddha Akṣobhya.)