Android 17 is Android 18's twin brother and the 17th creation of Dr.Gero he made his debut in the Android Saga when Dr.Gero raced to his lab to activate him and android 18 but soon they both betrayed him and Android 17 killed him by kicking off his head then squashing it then they activated Android 16 and went of there way but Vegeta cought up to them and battled Android 18 the two fought for fought till Android 18 injured Vegeta's arm then Trunks tried to kill Android 18 but 17 came down and delivered a jab to the back down went Trunks then he easily defeated piccolo and tien vegeta then tried to attack 17 but 18 knocked him down then instead of killing them they left but first 18 kissed krillin then after that they got in a van and drove to Goku's house but when they got there nobody was there then they went to Master Roshi's Island and piccolo said that he would take care of them but the to battled until cell aka Android 21 came and fought Android 17 and tried to absorb him until the time he almost did then Cell and Android 16 punched cell and the face then them to battled until Android 16 deliver the Hell's Flash then cell absorbed 17 and transformed he is killed when gohan kills Celll
-17 Android wikia

Short Summary and Super 17

human forcefully turned into a cyborg by Doctor Gero.[ch. 351] He and Android #18 are released by Doctor Gero as a last resort, but they turn on their creator and quickly kill him instead. They begin to travel in order to find and kill Goku, coming into contact with the main characters several times. In Future Trunks' timeline, he is a mass murderer who is later killed by Trunks. Android #17 returns in Dragon Ball GT, when he fuses with a new #17 created by Doctor Gero and Doctor Myuu in order to become Super #17 after dominating the z fighters Goku quickly gains the upper hand but after a kamehameha that Super 17 absorbed Super 17 defeats goku but when 18 appears she fires her infinity bullet Super 17 absorbs it but not paying attention to Goku Goku's dragon fist with a kamehameha at the end and super 17 was defeated but at the end of the shadow dragon saga when Goku wishes to revive everyone who was killed in the super 17 and shadow dragon saga and Android 17 lived on