One of the names of Śiva-Mahādeva (Siva-Mahaeva). In Chāndogya Upaniṣad (Chandogya Upanishad), Agni has been mentioned as Ī- kāra (I-kara). In Śaṁkarācārya’s (Sankaracharya) commentary on Chāndogya Upaniṣad , this self-manifestation of Ī-kāra had been discussed, but in later times, Paṇdita Ānandagiri (Pandit Anandagiri), while commenting on Śaṁkara’s annotations, has discussed it in greater details. The Sāmaveda (Samaveda)-songs in which Ī-kāra remains embedded, are imagined as the manifestations of Agni — ‘Īnidhanāiti. Īkaro nidhīyate yeṣu sāmaṣu anyāgneyāni prasiddhāni‘. Fom this concept, Agni has been imagined as Ī-kāra in Chāndogya Upaniṣad.
Since the Vedic era to the Paurāṇika (Pauranika) times, God Śiva (Siva) has often been imagined as having an entity that is inseparable from Agni. So naturally, Agni’s manifestation as Ī-kāra has been attributed to Śiva.