The human scientist Zero aids in Mega Man Zero is Ciel.
Ciel is a scientist who leads a resistance movement against Neo Arcadia, a supposedly ideal society that oppresses and destroys Reploids. At the beginning of the game, she and her companions are pursued through an abandoned laboratory and find Zero sealed away after roughly a century in stasis.
Ciel's Cyber-elf, Passy, sacrifices itself to awaken Zero. Although Zero is initially amnesiac, Ciel explains the crisis facing Reploids and asks for his help. Zero then joins her Resistance, carrying out missions while Ciel works on a new energy source intended to give humans and Reploids a safer place to live.
The game is set about 100 years after the Mega Man X series. Layer, Alia, and Iris are also associated with the wider Mega Man X universe, but they are not the scientist Zero assists in this story. Ciel's research and decisions are central to the game's political conflict and later revelations about Neo Arcadia.