A mighty असुर . This असुर lived inside a conch. श्री कृष्ण killed this असुर .

श्रीकृष्ण and बलभद्रराम were having their education in the आश्रम of the sage सान्दीपनि . On the eve of their completing their education an असुर named पञ्चज carried away the son of the sage while the child was bathing in the प्रभासतीर्थ and kept him inside a conch where the असुर lived. The sage, greatly griefstricken asked his disciples to get him back his son as his गुरुदक्षिणा (fees for the preceptor). Accordingly श्रीकृष्ण and बलराम went to the banks of the river and prayed to वरुण . वरुण appeared before them and then they told him about the mishap. With the help of वरुण they killed the असुरपञ्चज and got back the son of their guru. The conch in which the असुर lived was taken by कृष्ण . Because the conch belonged to पञ्चज the conch got the name पाञ्चजन्य . (10th Skandha, Bhāgavata)

सगर of the solar race got a son named असमञ्जस of his wife केशिनी . He became famous as पञ्चज . He was the father of अंशुमान् and grandfather of दिलीप . (Chapter 15, Harivaṃśa) .