Knife is an assassin employed by The Many Arms of Death and an enemy of Batwoman. A rather stoic and humorless woman, she holds Kate Kane personally responsible for the so-called "taming" of Coryana, which ruined the island's reputation as an independent haven.
Knife abandoned her old name of Tahani after becoming an assassin. As her name indicates, she prefers bladed weapons.
Not much is known about Knife's backstory. She is likely Nigerian, having lived as a beggar in the city of Ibadan. One night, after murdering a man for a small bit of food, Tahani was approached by Safiyah Sohail, the de facto leader of the island nation of Coryana. The man Tahani had just killed happened to be a troublesome business associate of Safiyah's, and she appreciated Tahani removing him. Safiyah offered Tahani a new, better life on Coryana, and Tahani accepted.
Tahani lived for an unspecified period of time on Coryana before the accidental arrival of Kate Kane, who practically washed up onshore after a diving accident and was taken in by Safiyah. Tahani seemed to be jealous of Kate and Safiyah's growing romance.
After Kate had been on the island for about a year, she and Safiyah had some sort of falling out, which lead to Kate leaving and Safiyah eventually disappearing. This in turn lead to outside corporate interests taking root on Coryana now that Safiyah was no longer around to unite the island's various warlords and push back.
Roughly six years later, Tahani had become an assassin and dropped her old name. She lured Kate Kane to Coryana in an attempt to eliminate her at the behest of The Many Arms of Death.