Trinity refers to the three main idols of Sri Jagannatha Temple. They are Sri Jagannatha, Sri Balabhadra, and Sri Subhadra. On the Ratnta Singhasana in the sanctum sanctorum, all three idols are worshipped along with Sri Sudarshana, Goddess Bhudevi, Sridevi, and Lord Madhava.
Many Thinkers and researchers consider, Sri Jagannatha as Sri Krishna and Balabharda as his elder brother, and Subhadra his sister in this trinity concept but others believe Sudarshana is also a part of Vishnu and they call this combination as Chaturdhamurti.
In Chatirdha Murti concept: Lord Jagannatha is Sri Vishnu, Balabhadra is Ananta Naaga, Subhadra is Goddess Laxmi and Sudarshana is the great disk.

As per Skandha Puran, Lord Bishnu himself has made the deities. He came in disguise as an old man to King Indradyumna, who was here in puri to establish this important Hundu region from the then Malaba ( now Ujjain). At that time King was in tremendous pressure and trouble and unable to decide the shape of the god. This old man said I can made the god’s shape in 21 days but no body should disturb him. Even he will not take any food or water during this time. The king said yes and the old man locked the door.

After 15 days but he Queen was shocked by not listnening any sound from the room. She appealed and requested the king to open the door as she doubts any threat to the life of the old carpenter.

Then the king opened the door. Saw half made idols and no carpenter there. He searched again and again, cried and listened a sound from the sky that he remained half made by his wish only, this is the shape to be worshipped in future and the carpenter was nobody, he himself. “ So, O’ king don’t repent, now make this temple as the Hindu centre of excellence”. Then Raja Indradyumna came out and made arrangements for the worship.

History says different. It drags us to the period of 3rd Anang Bhima deva. Near about 1237, he replaced the old idol of Laxmi Purusottama and started worshipping the trinity. Then the three idols named as Hali, Chakri and Subhadra. As Balabhadra holds hala & Mushala, he is called as Hali. Similarly Jagannth was called as Chakru=I as he holds the dish or sudarshan Chakra.

This initiate helped the governance system to maintain an equilibrium among the three major sects of Hindu community.