According to Onam mythology and popular belief, Lord Vishnu in his Vamana Avatar unjustly pushed King Mahabali into the netherworld or pathalam. But Lord Vishnu granted King Bali the boon to visit his subjects once in a year. It is also believed that King Bali got ‘Vishnu sayujyam’ or reached the Vaikunta. Due to this both King Mahabali and Lord Vishnu in the Vamana avatar are welcomed during Onam. This makes Onam a unique festival in which the victor and the vanquished are both are worshipped.
The structure is made using clay or mud and generally it has four faces with a flat top. In some places the structure is in the shape of a cone. Nowadays readymade Thrikakkarappan structures are available for sale during Onam festival.
While welcoming King Mahabali to the homes, people place Thrikkakara Appan on a bed made of rice flour and is decked with flowers and pujas are performed. It is also placed along with the Athapookalam – the special floral arrangement done during Onam. Some people believe that the unique shape of Thrikkakara Appan – the four faces – represents the four stages in the life of a man. Usually, people place three structures which represent the three steps of land asked by Vamana to King Mahabali.