Soorapadma, Singamukha, and Tarakasura were mighty demons, born to sage Kashyapa by his liaison with the demoness, Maya. As advised by Asura Guru Shukracharya, these brothers performed severe penance towards Lord Shiva and obtained from him, many fantastic boons. The chief among those assured them that they can meet their end only at the hands of the son born to Shiva himself and that he should also be not the one born out of a woman’s womb.
This made them invincible, or at least that was what they thought when they sought and obtained such a boon from the Lord. They had reasons to believe so, for Shiva undertook a severe penance around that time and seemed to be too engrossed in it to get distracted by any means. Hence there looked to be no way that he can father a son who can really challenge these demons.
Emboldened by the strength of the boons, the demons unleashed a reign of terror on all the worlds, putting the Devas, human and all other beings to untold hardships, and there seemed to be no end in sight to their tyranny.
But events do not always go on as planned or anticipated. This turned out to be so in this case too.
Realizing that only Shiva can protect them from such repression let loose by the demons and that too should happen only in the form of an issue from him, the Devas worked out a plan. Accordingly, the cupid Manmata, the God of love will disturb Shiva’s penance so that he will open his eyes, cast a loving glance on Parvati, who was serving him with devotion then and their union will result in a mighty son, who can rid them of their problems.
As requested by the heavenly beings, the God of love very dutifully shot his beautiful flower arrow from his famed sugarcane bow at the Lord immersed in penance. Shiva was rudely shaken awake and in a moment of intense anger opened his fiery third eye, which burnt down Manmata to ashes. The Devas were not prepared for this tragic turn of events, fell at the feet of the Lord, sought his pardon and pleaded for the life of Cupid, who did what he did only to help them out. The compassionate God brought Manmata back to life and made him visible only to his spouse.
To help out the Devas, Shiva then opened his third eye, and a blazing flame emerged out of it. The divine forces carried this to the sacred pond, SaravanaPoigai, where, the fire transformed into six sparks and six handsome male babies emerged out of them. These divine infants were well taken care of by six angels known as Karthigai damsels, who were nothing but the personifications of the great star Krithigai. As Goddess Parvati very fondly hugged the six young ones together, they all merged into a single form, with six heads. Thus was born Muruga, who is also called in many other names such as Skanda, Subramanya, etc. He also got the name Kartikeyan, as he was raised by the Karthigai damsels and Shanmuga, as he has six heads or faces.
Muruga then went ahead, took on the might of the demon army led by the 3 Asura brothers, fought a fierce battle with them for five days and annihilated evil comprehensively on the 6th day. This day of his stupendous victory is celebrated as Skanda Shasti.