Cell is a character and one of the three main villains of Dragon Ball Z. He has four total forms but is most recognizable in his Perfect Form. He appears in the middle of the Android Saga of Dragon Ball Z and quickly becomes the main villan after absorbing Androids 17 and 18. He proves to be very strong in his Perfect form, far stronger than a Super Saiyan,as shown when goku and gohan try to fight him and so in order to defeat him, Gohan must transform into a Super Saiyan 2.
After he reaches his 4th Form (not exactly a form, just a stronger version of the original perfect form) he becomes as strong as or maybe even stronger than a Super Saiyan 2. He is finally defeated by Gohan in the an epic kamehameha wave battle between the Solar Kamehameha and the Father Son Kamehameha.
His first form is known as Imperfect Cell, his second form is known as Semi-Perfect Cell, his third form is known as Perfect Cell and forth form is known as Super Perfect Cell.