Vallavarayan Vanthiyathevan was a real personality who existed in Chola regime under Raja Raja Chola I and before. His origins and clan are subjects of great debate. Sadasiva Pandarathar suggests that he might have belonged to eastern chalukya but without offering much evidence to support his claim. From evidences gathered so far he is a Rashtrakuta king and absolutely nothing to prove his connectivity with Vaanar Kulam. We don't know why Kalki Krishnamurthy strongly believed his clan is Vaanar Kulam (Bana Kingdom) and depicted the same in his famous novel Ponniyin Selvan.
To add more evidence that he is a Chalukyan, if you look at chola dynasty since Adithya Chola it has been a trend to strengthen their ties through marital alliances. Right from Adithya, Paranthaga and Sundara we see kings marrying many daughters, sometimes from potential would-be enemy empires and forge solid relationship with them. And in case of Vanthiyathevan, we see that he married Kundavai, perhaps the most powerful princess of her times. It's worthwhile to ponder whether this had any gains to chola empire. In this light, it makes sense to view Vanthiyathevan as an east chalukyan prince, because later we see Raja Raja Chola Iforging very strong relationship with them by giving his daughter to Vimaladitya, who is of chalukyan origin. (This resulted in a completely different set of chola-chalukya clan, from the time of Kulothungan I). It is evident that Rajaraja would not have experimented this marriage unless he had a strong faith in their relationship. This could have been due to Vanthiyathevan.
Coming to the Vanthiyathevan character which Kalki Krishnamurthy created for his famous novel Ponniyin Selvan, the first thing that should be held in mind is that, initially he was not intended to be a hero. Kalki wanted to sideline him, just like Paranjyothi of Sivakamiyin Sabatham, after making use of him to introduce the characters and places. But it so happened that the character grew steadily on his own might, and in spite of the elaborate introductions, Arumozhi failed to capture the hearts of people as much as Vanthiyathevan did. In fact, in certain portions where Vanthiyathevan is not featured for several chapters, his absence can be noticed so vividly that during his reappearance Kalki will write, "We have deserted our hero for a long time..." This is the first occasion in which Kalki recognizes him as the true hero of this story. This is a typical example for the case in which imagination triumphs over its own creator.
Vanthiyathevan is closer to life than ever perfect Arumozhi. He makes many mistakes; he is quick in decisions and is often proud about his good looks. He undergoes the pleasures and pains of royal service. He is a true friend and a sincere lover.
As we read more and more of history, the young, adventurous, naughty, lucky and attractive portrayed in Ponniyin Selvan was Kalki's brainchild, Vallavarayan Vanthiyathevan just being a name borrowed from the pages of history to attach credibility to the character he created. He seems to have ruled a region callen Bramadesam and around living with his wives and Kundavai spent most of her time in Thanjavur.
His name is referred in Thanjavur Big Temple inscription in which he is referred to as the husband of Kundavai Pirattiyar. A life sized statue depicting Vanthiyathevan controlling a horse is erected in Chennai near Anna Flyover in Mount Road as an honour to this great personality during the first tenure of Mr. Karunanidhi as Chief Minister (This was to capture the banning of horse race by the the government of Tamilnadu is a different background altogether)