Literally, translated, Karuppanaswamy means , “Dark God.” Revered as the ‘Kaaval Deivam’ (God of Protection) across TamilNadu, He drives away the forces of evil, falsehood and treachery.
Sporting a thick moustache, riding a white horse and carrying a whip in his right hand, He is a fierce warrior, who punishes those who harass his devotees.  
He protects His devotees and ensures justice and self discipline amongst His devotees.  
He is said to ride on His horse through the entire area, blocking the entry of any evil across the entire landscape.  
The Legend of Lord Karuppanaswamy
There are various legends in Hindu mythology about Lord Karuppanaswamy.
1. He is said to have sprung from Lord Vishnu’s hands and hence is also known as Kaiyannar (One Created from the hand).
2. According to another legend, Lord Rama had sent Devi Sita to the forest when she was pregnant and lived in Saint Valmiki's Ashram. While in the Ashram, she gave birth to a male child.

One day when she was going out for some chores of the Ashram, she asked the Saint to take care of her child in the cradle. The Saint was watching the child and meanwhile went into a deep meditation. When Devi Sita returned, she found that the Saint was in meditation and didn't want to disturb him to tell him that she was taking her child.  

When the Saint was out of the meditation, he found the child missing. So he put some holy grass (Dherbai) in the cradle and with his mantra he made that as a child.  
Later when he found that Devi Sita was having her real child, he asked Devi Sita to treat the new baby also as her own child.  

Lord Rama was surprised to find two boys (Lavan and Kushan) with Devi Sita. To test the purity of the boys, he set a fire and asked the boys to cross the fire to reach Him. He told that whoever was his real heir would cross the fire unscathed. Unknowingly the boy brought up by the Saint, got stuck in the middle of the fire and burnt his body becoming very dark.  

When Lord Rama was informed of the incident in the forest, He blessed the burnt boy to become his Escort God (Kaaval Deivam) and called him “Karuppannan.”  

That is the reason why Lord Karuppanaswamy has the Thiru Namam on his forehead.  

Many temple priest still sing the devotional song “Dherbaiyil Pirandhavane" (born from the holy grass) in praise of Lord Karuppanaswamy.  
3. According to a third legend, He is one of the 18 sons of Lord Krishna. Hence He is also referred to as “Shyamala Krishna Putra.”