Hell Fighter 17 is the identical android created by Dr. Gero and Dr. Myuu. His debut is in the episode " A Dangerous Union".
Becoming Super 17 Edit
Hell Fighter 17 influences the original 17 to fuse to create Super 17, first, he sent 17 to hypnotize 18 into becoming one of them, but Krillin brings her back, leading Android 17 to kill him, angering 18 to attack 17, but to no avail. He heads off and proceeds with Hell Fighter 17's plan. Later, he fuses with 17 to create Super 17, the ultimate android