Īśvara 自在 (Sanskrit Īśvara “Sovereign”, honorifically the bhikṣu 比丘 in the colophon — hence often given as 自在比丘 or 比丘自在) was an Indian Buddhist ācārya of uncertain dates, presumably of the late Madhyamaka period (sixth or seventh century). He is known to East Asia exclusively as the author of the prose commentary (vyākhyā) on Nāgārjuna’s Bodhisaṃbhāra-śāstra — preserved only in 達磨笈多’s Suí-period Chinese translation as the Pútí zī-liáng lùn 菩提資糧論 (KR6o0065). The Tibetan tradition does not attest a parallel commentary, and no biographical information is available beyond the colophon. He is not the same as the Madhyamaka logician Īśvarakṛṣṇa, nor as the Hindu deity Īśvara.
Note: The same Chinese name 自在 occasionally surfaces in Chinese Buddhist sources for other Indian masters (a number of late-period paṇḍitas bore this honorific name); without disambiguating dates or contextual cues, this person should be understood as the commentator on Nāgārjuna’s Bodhisaṃbhāra preserved in KR6o0065.