Originally, Spiderman would have discovered that his black suit is an alien symbiot which would permanently bond with his body, and that this symbiot is pregnant, and about to spawn another symbiot, to be forcefully bond with Spidey’s girlfriend, Mary Jane.
So Spiderman takes initiative and tries to kill the symbiot, doing it using a loud noise. The symbiot suit is forcefully removed from Peter. The symbiot’s spawn is killed by the noise, but the symbiot itself survives barely and slithers away.
Some time before that, Spiderman was fighting a villain above the streets of New York, which distracts a Taxi driver who crashes into the Taxi in front of him. Inside that taxi was a couple, and the wife was going into labor. The driver, husband, and unborn child die, but the woman survives, and resents Spiderman, blaming him for this.
The weakened symbiot finds that woman, and identifies with her sorrow over her dead unborn child and husband, and her hate towards Spiderman, and she willingly fuses with the symbiot, creating Spiderman’s strongest foe yet.