Which sage is traditionally credited with spreading Vedic culture (Aryanisation) in south India?

The sage Agastya is traditionally credited with spreading Vedic culture and Sanskrit learning to south India.

Legends of Agastya:

• He is said to have crossed the Vindhya mountains to go south.
• According to a famous legend, the Vindhya mountains kept growing taller; Agastya asked them to bow down to let him pass, and to stay low until he returned; he never returned, so the mountains remained low.
• He is also said to have drunk up the ocean to help the gods find demons hiding in it.
• He is believed to have settled in the south, in the region of the Pothigai (Agasthyamalai) hills in the Western Ghats.
• His wife was Lopamudra, who is also said to have composed hymns of the Rigveda.

Agastya in the Rigveda and epics:

• Some hymns of the Rigveda are attributed to him.
• In the Ramayana, Rama meets Agastya in the forest, and Agastya gives him divine weapons; he also teaches Rama the "Aditya Hridayam" hymn to the Sun before the battle with Ravana.

Agastya in Tamil tradition:

• He is regarded as the founder of Tamil grammar; according to tradition, he wrote the grammar "Agattiyam", which is now lost.
• He is revered as one of the "Siddhars" (Tamil saints and physicians), and is associated with Siddha medicine.

Places named after him:

"Agasthyamalai" (Agastyarkoodam) peak and the "Agasthyamalai Biosphere Reserve" on the Kerala-Tamil Nadu border, which is part of UNESCO's World Network of Biosphere Reserves (2016).

Spread of Vedic culture in the south:

It happened gradually, through migration of Brahmanas and the patronage of rulers, from the later Vedic period onwards.

Why not the other options?

• ✗Vasishtha, Vishvamitra and Bharadvaja were sages associated with the Rigvedic tribes of the north.