There is no root deity of Jambavan. Every Vanara was created by some deity taking inspiration from Jambavan himself. Jambavan was created suddenly from Brahma's yawn.
From Valmiki Ramayana Bala Kanda Sarga 17 (Translated by Desiraju Hanumanta Rao & K. M. K. Murthy)
pūrvameva mayā sṛṣṭo jāṃbavānṛkṣapuṅgavaḥ |
jṛṃbhamāṇasya sahasā mama vakrādajāyata || 1-17-7
te tathoktā bhagavatā tat pratiśrutya śāsanam |
janayāmāsurevaṃ te putrān vānararūpiṇaḥ || 1-17-8
"I have already created the eminent bear Jambavanta in earlier times, as he suddenly came forth from my yawning face. [1-17-7]
When Brahma addressed them thus, those gods have agreed to his order and accordingly started to parent sons in the resemblance of monkeys. [1-17-8]