Mūlavar — The Immovable, Eternal Presence
Mūlavar ('the original/root one, the founding deity') is the term for the principal consecrated form (vigraham) of Emperumān who permanently resides in the innermost sanctum (garbhagṛham) of a Śrī Vaiṣṇava temple. The name reflects both primacy (being the original, founding presence of the kṣetram) and immovability — the mūlavar never leaves the sanctum, never participates in outdoor processions, and is always accessible to devotees within the inner shrine.
The mūlavar stands in a carefully defined posture (tirukkōlam) that carries theological meaning: most commonly the śayana (reclining) posture (as at Śrīraṅgam's Periya Perumāḷ), the sthānaka (standing) posture (as at Tiruveṅkaṭam's Śrīnivāsa), or the āsīna (seated) posture — each reflecting a particular aspect of Bhagavān's sovereignty and grace.
In Śrī Vaiṣṇava theology, the mūlavar represents Bhagavān's nitya (eternal) presence at the kṣetram — His unchanging, sovereign dwelling place. The utsavar (festival image) who goes out in processions is the mūlavar's 'representative,' taken to the streets out of compassion to be seen by those who cannot enter the inner shrine. The mūlavar is the principal immovable deity of a temple, whether or not that temple is a Divya Desam. A shrine is classified as a Divya Desam because it received Āzhvār maṅgalāśāsanam, not merely because a mūlavar is installed there.
The posture, ornaments, weapons, and associated consorts of the mūlavar at each Divya Desam carry specific theological significance elaborated in the Āzhvārs' pāsurams and the Āchāryas' commentaries. The specific maṅgalāśāsanam (benediction) sung by each Āzhvār at each kṣetram is addressed to that particular mūlavar — making the 4,000 pāsurams of the Divya Prabandham, in part, a continuous theological meditation on the specific manifestations of Bhagavān across 108 sacred sites.