Ahamkara in Hinduism is the shape that self takes. It is the principle of individuation developed out of buddhi. According to Samkhya, the development of the process of evolution follows a law of succession. Here, mahat (the great) is the first product of evolution of prakriti. It is the basis of buddhi (intelligence) of the individual. Mahat brings out the cosmic aspect, and buddhi, the psychological counterpart of mahat in the individual. Buddhi is the subtle substance of all mental processes.
Ahamkara is the I-ness which gives rise to different kinds of evolutes, according to the dominance of sattva or tamas. The set of eleven attributes abounding in sattva evolves out of vaikrta form of the I-principle; a set of rudimentary substances from bhutadi form of the I-principle; and both of them form the taijasa form of the I-principle. When ahamkara is dominated by sattva attitude, it is called vaikrta.
Ahamkara, according to advaita Vedanta, is I-hood, egotism and spiritual ignorance. It is one of the four antahkaranas (internal organs) along with manas, buddhi, and chitta.
Antahkarana is the cognizing apparatus, the inner base of thinking and feeling. Mula prakriti with avidya is termed as ahamkara (I-ness). Antahkarana is one but called by four names according to the four functions it performs – mans, buddhi, ahamkara and chitta.
Ahamkara is said to be vritti (the mode) of antahkarana. Sadananda, a Advaitin, does not accept buddhi and manas and adjusts the two, chitta and ahamkara in buddhi and manas, respectively.