I will tackle other unpopular theories later. This Narakasuran turns out to be the son of Vishnu himself during Vishnu's Varaka Avatar and Bhooma Devi.
Avatar is a sort of incarnation.
Sathyabama, Krishna's consort in Krishnavatar is Bhooma Devi. So, this Narakasuran grows up and up and up as is usual in our myths, and becomes a demon, pleases Brahma and gets great great powers and follows on the path of demons and starts hitting the good people on earth and all that. So, people, as is usual go to Krishna and tell him about the innumerable hardships they go through because of this oversize asuran. So Krishna decides to get rid of this bad guy and kills Narakasuran-his own son. Sathyabama looks on, stomachs the sorrow of seeing her flesh and blood being killed by the father, on Krishna Patcha Sathurthasi day.