Kṣīrodakaśāyī-Viṣṇu is one of the puruṣa Āvatāra of Nārāyaṇa.
In Gauḍīya Vaishnavism, a school of Vaiṣṇavism, the Sātvata-tantra describes three different forms, or aspects, of Vishnu as Mahavishnu, Garbhodakśayī-Viṣṇu and Kṣīrodakaśāyī Vishnu. Kṣīrodakaśāyī-Viṣṇu resides in the heart of every living creature as a four hand expansion similar to that of Mahāviṣṇu. He is also referred to as Paramātmā or super soul. His abode is the Vaikuṇṭha.
Sattva guṇa
The Viṣṇu or the Deity of the quality of goodness in the material world is the puruṣāvatāra known as Kṣīrodakaśāyī Viṣṇu or Paramātmā.
References
Ksirodakasayi Vishnu Wikipedia(Text) CC BY-SA