6. Deathstroke/Slade Wilson
Having a history with Oliver Queen, Slade Wilson was a man driven by a need for revenge. He was a villain who was closely tied to our leading man, and that made him especially dangerous.
The fact that these two had a strong bond with each other also made it even more heartbreaking that they were on opposite sides. When Oliver thought Slade was dead, he moved on with his life, and yet Slade didn’t. Instead, he used his own anger, pain, and sense of betrayal to become the kind of villain that thrived on Arrow.
There were plenty of times when Deathstroke would go head-to-head with Arrow and when he finally had the chance to destroy Oliver he didn’t take that chance, instead being responsible for a death that sent shockwaves through the Arrowverse.
While Slade and Oliver did come to an understanding, these two could never have the relationship they once did, which is a tragedy in itself. The history between these two men was enough to make them the perfect hero versus villain pairing. And considering Deathstroke is a character who has made an impact on the greater DC Universe at large, Manu Bennett will perhaps live on as one of the best actors to play the part.
Honestly, I think it was a mistake for the series to remove Deathstroke from the picture and there are plenty of fans who felt the same way.