The version of Cell that plays a large role in Dragon Ball Z hails from an alternate future timeline where he has already evolved to his Imperfect form. Unfortunately for him, neither Future Android 17 nor Future Android 18 are present, having already been taken out by his version of Future Trunks. In order to complete his evolution, Cell kills Future Trunks and steals his Time Machine, going back in time to the date set by Future Trunks in the "standard" timeline when both Androids are still functional, sometime around four years prior to the Androids' arrival. In order to fit into the machine, Cell has to revert back to an egg.
Once in the past, he hides underground for four years until he can grow back to his adult, humanoid self. After emerging in his Imperfect form, Cell still fears that he does not have the power he needs to forcibly absorb the Androids. To increase his strength, his first actions are to exterminate several towns, absorbing the human inhabitants within. After completing his feeding on the humans in Ginger Town, Cell is confronted by Piccolo. While Piccolo wonders who Cell is, Cell reveals that he himself knows of Piccolo's identity as the Demon King Piccolo. After a brief struggle where he is beaten around several times, he manages to absorb enough of Piccolo's power to make himself stronger, draining the biomass from one of Piccolo's arms. Cell explains who he is to Piccolo. After hearing the story of his creation and his plan, Piccolo reveals that he tricked Cell to give him the time he needed to regenerate his arm and allow him to continue fighting. Future Trunks and Krillin then arrive at the scene. Future Trunks' presence in the past surprises Cell, as is the fact that Goku has not died of his heart disease and is still alive. Outnumbered, Cell quickly uses the Solar Flare to temporarily blind his opponents and escape, masking his energy to prevent them from finding him.
Realizing that he is still far below his enemies' power levels, Cell decides to use a hit-and-run strategy at this point, hiding from the Z Fighters while going from town to town absorbing humans and gaining the power he needs to be able to take on the Androids. Piccolo and Tien work on tracking him while Future Trunks and Krillin kill the current timeline's Cell while still in his infancy. Eventually, after absorbing several tens of thousands of humans, Cell detects a large ki; knowing that this has to be Piccolo, he deduces that the only thing that could make him fight so hard would be the Androids. Gleeful at the oppurtunity to finally absorb 17 and transform to a stronger state, Cell wastes no time and quickly heads toward the area. As expected, he finds Piccolo and Android 17 engaged in battle.
Cell interrupts the fight and attacks Android 17. At this point, his power has far surpassed Piccolo and Android 17's, and without any precautions, he approaches 17. As the monster prepares to absorb the Android, Piccolo attacks him, freeing Android 17 from his grasp. When Android 17 learns what Cell has planned, he dismisses the threat, thinking that he is much more powerful than Cell could ever be, and attacks. After knocking away Android 17, Cell fights and easily beats Piccolo, even managing to shrug off the Namekian's Light Grenade. After blasting a hole through Piccolo's side and tossing him into the sea, Cell is able to attack 17 again.
He has almost absorbed Android 17 when Android 16 becomes involved. Android 16 states that according to his calculations, he is just equivalent to Cell in both strength and speed, and portends that he will be the one to kill Cell. After a struggle where it is revealed that Cell is unable to absorb Android 16's energy, 16 force Cell belowground and blasts him using his Hell's Flash . Before Android 16 can finish Cell off, Android 17 interrupts and remarks that the three of them are unbeatable.
Cell uses this opportunity to burst out of the ground directly behind Android 17 and, whilst sadistically laughing, he quickly absorbs Android 17 and evolves into his Semi-Perfect form. [Source: wikia]
About the Dragon Ball paper model:
Size: 36 cm
Format: .pdo line + lineless
You can download the papercraft model here: Dragon Ball - Chibi Imperfect Cell (First Form) Free Papercraft Download