(The TH in this name is pronounced as 'th' in 'with' and KSH as 'ctio' in 'action'.)
See the link 'naaga' too.
Thakshaka was a serpent lord. He was a prominent one among the naagas of the underworlds. In Mahaabhaaratham, many naagas wee mentioned. But Thakshaka was mentioned in the very beginning itself. In fact, one of his acts became the prime reason for the recital of Mahaabhaaratham to Janamejaya.
After the paandavas, Pareekshith, the posthumous son of Abhimanyu, succeeded their throne at the age of 36. He ruled for 60 years. In his last days, once he went to a forest for hunting. Becoming thirsty, he went to sage Shameeka's hermit nearby, for water. But the sage was in deep meditation and so he did not see the king or invite him. Pareekshith became angry with that (what he felt as ) negligence. He lifted a dead snake lying around with his bow-tip and hung it around the neck of the meditating sage. The sage was still in his yogic trance. Pareekshith went on his way.
After some time, shameeka's son Shringi came home and saw the insult made to his father. He turned furious over the undeserving mean act of the king and cursed that Pareekshith would fall victim to serpent Thakshaka on the seventh day from that day. Shameeka woke up from his trance and learnt what had happened. He reprimanded his son for turning slave to anger which never befits a sage and sent a word to Pareekshith through his disciple Gouramukha,about Shringi's curse.
Pareekshith made enormous arrangements to save himself from Thakshaka's bite . He constructed a single coloumn buiiding and stayed in it under day and night guard, keeping with him many expert curers of snake-bite. He was listening to the recitalof Mahaabhaagavatham by sage Shuka. Meanwhile Thakshaka went to bite Pareekshith, being prompted by the power of Shringi's curse. In the way he met a braahmana named Kaashyapa who was gifted by Brahma with a magical art of reviving any thing that was killedby snake-bite. Learning that the braahmana was going to save Pareekshith with his powers, Thakshaka convinced him that destiny was beyond his control and sent him back giving him a lot of money.
Thakshaka devised a plan to approach Pareekshith's well protected residence. He waited upto the fag end of the seventh day. Then he sent some naaga youth in the guise of braahmanas to see the king to offer him a variety of delicious fruits and fragrant flowers, he himself following them invisibly. Pareekshith allowed them in all trust. He felt that the danger was over, as the seventh day was drawing to close and he took one of the fruits and peeled it to eat. Thakshaka came out of the fruit in the form of a minute insect, turned in a flash into a gigantic snake of red colour and bit Pareekshith. Everything was done in a fraction of a second.The onlookers were terrified at the horrid scene and took to their heels. The king and his building were burnt into ashes with the power of the venom of Thakshaka. thus Pareekshith could not escape from Shringi's curse. Janamejaya, aged 25 then, started his rule after his father was thus killed.
Also, once when a sage Udanka was bringing ear-rings for his teacher Pyla's wife from king Poushya's queen, Thakshaka stole them in the way. Udanka went into Paathaalam with the help of Indra and terorised all the naagas. Thakshaka brought the ear-rings and gave to Udanka. After completing his teacher's work, Udanka went to Janamejaya. He told Janamejaya how Thakshaka killed Pareekshith and provoked him to undertake destruction of all the serpents through a sacrifice named Sarpayaaga. Janamejaya too, wanted to revenge his father's killing and started the sacrifice. As the sacrifice progressed, various snakes from various places belonging to various sects of naagas came off and fell in the altar fire. Thakshaka went to Indra begging safety. The conductors of the sacrifice understood that Indra harboured Thakshaka and they chanted hymns offering Thakshaka with Indra as oblation to the gods. As Thakshaka was being pulled by the power of the chants of the braahmanas despite Indra's attempts to save him, a sage Aastheeka went to Janamejaya, at the behest of the naaga chiefs. He convinced Janamejaya to drop his sacrifice in the middle, thereby protecting the rest of the naagas. After the sacrifice was dropped i the midddle, Janamejaya asked sage Vyaasa about the rift between the paandavas and the kouravas. Vyaasa employed his disciple Vyshampaayana to relate the entire epic of Mahaabhaaratham. Sootha, also known as Ugrashravas, heard that recital and he retold the epic to the group of sages Shounaka and oters at the Nymiaha forest. That way, we are given this great epic.