Android 17 suddenly became one of the strongest heroes in the world of Dragon Ball when he was brought back for Dragon Ball Super’s Tournament of Power. … Android 17 was matched up with Piccolo (who he was unable to beat) and absorbed by Cell.
Why do Android 17 and 18 hate each other?
Later at some point when they were about 17 y/o Dr Maki Gero kidnapped them and transformed them into androids. 17 and 18 held a HUGE GRUDGE against him. They did not want that. So they took revenge on him.
Why is 17 so strong?
Android 17 was so powerful in Super for nearly the same reason that when Frieza and even Fat Buu trained they got a massive power boost. Their base is already massive without any training. Android 17 is organic and mechanical, so he has potential to increase his power through training.