SPOILER WARNING: This article contains major spoilers for "Due Process," the latest episode of Arrow.
When Felicity broke bad and became a villain, she found a few villainous compatriots to aid her quest. In "Due Process," the latest episode of Arrow, William and his ragtag group of vigilantes discovered she had been working with Blackstar to blow up the parts of Star City not overrun by the Glades.
Created by Paul Kupperberg and Carmine Infantino in 1983's Supergirl #1, Blackstarr was a codename for Rachel Berkowitz. As a young girl, Berkowitz was brought to a concentration camp, but she delighted the camp's commander, who brought her home to live with him. After getting her PhD, Berkowitz conducted an experiment that resulted her the ability to manipulate matter and energy. With these powers and her Nazi beliefs, she became the villain known as Blackstarr. She and Supergirl went toe-to-toe in the "Blackstarr" storyline.
Notably, Blackstarr also appears in Crisis on Infinite Earths, from which this year's three-show crossover Elseworlds draws inspiration. She aided Superman and Supergirl before she disappeared; she has not returned to the comics since.
As Blackstar did not appear in person during "Due Process," it is unclear how she will continue to influence the flash forwards. However, her mention is significant and suggests William and his team may track her down to learn more information about Felicity's mysterious plan.
Airing Mondays at 8 pm ET/PT on The CW, Arrow stars Stephen Amell as Oliver Queen, David Ramsey as John Diggle, Emily Bett Rickards as Felicity Smoak, Rick Gonzalez as Wild Dog, Echo Kellum as Mr. Terrific, Juliana Harkavy as Black Canary, Colton Haynes as Arsenal, Kirk Acevedo as Diaz and Katie Cassidy as Black Siren.