Bhagavad Gita · Karma YogaChapter 3, Shloka 27 (3.27)

Who is the doer? According to the verse: the gunas of prakriti (sattva, rajas, tamas) — which work in the form of the body, the senses and the mind. "I am the doer" — this is the illusion of ego.

Shankaracharya: Prakriti = sattva-rajas-tamasāṃ guṇānāṃ sāmyāvasthā — the balanced state of the three gunas; its gunas = vikāraiḥ kārya-karaṇa-rūpaiḥ — their transformed forms, as the body and the senses. Worldly and scriptural — all actions come from them alone. One deluded by ego, avidyayā karmāṇi ātmani manyamānaḥ — attributing actions to the self through ignorance (avidya), thinks "I am the doer".

Acharya Ramanuja: prakṛteḥ guṇaiḥ sattvādibhiḥ svānurūpaṃ kriyamāṇāni — the gunas, sattva and the rest, perform actions in keeping with their own nature; ego = the sense of "I" in prakriti, which is not "I"; because of it, one who is ajñātātma-svarūpaḥ — who does not know the nature of the self — thinks "I am the doer". Ramanuja makes clear at the end of 3.29: the self's agency is not svarūpa-prayukta (from its own nature) but guṇa-sambandha-kṛta (brought about by its connection with the gunas) — that is, Ramanuja does not wholly deny the self's agency, but regards it as based on the gunas and (in 3.30) on the Lord.