I've always considered Merlyn to be Ollie's arch nemesis. Ollie does also have a long-running feud with Deathstroke.

Originally it was Count Vertigo but in modern days it has shifted to Merlyn

I've always considered Merlyn to be Ollie's arch nemesis. Ollie does also have a long-running feud with Deathstroke.

Clock King

either deathstroke or merlyn. My definition of arch-nemisis is someone who will attack the hero for no reason other then to ruin their lives, EX: Joker, Captain cold, Black Manta, so that would mean either of those 2

Count Vertigo or Merlyn.

His number 2 and 1.

Count Vertigo or Merlin.

Deadshot

When most people think of his main villain its either Count Vertigo or Merlyn because he has a bit of a long history with both of them.

In the silver age, it was Clock King. In the bronze age, new villains were invented such as Merlyn, Slingshot, Vertigo and Stinger. Merlyn started in JLA. Slingshot was used a few times in World's Finest dollar comic. Vertigo and Stinger started at the same time. Black Canary fought Vertigo first in an issue of Worlds Finest dollar comic in her own solo feature. In the Green Arrow solo feature, Green Arrow fought new villain Stinger. In the next issue, Vertigo teamed up with Stinger to fight Black Canary and Green Arrow. Vertigo soon became a popular Green Arrow villain and was used in the first Green Arrow mini series. Deathstroke also started in the bronze age as a Teen Titans villain. Deadshot was revived in the bronze age to fight Batman.

http://en.wikipedia.org/wiki/List_of_Green_Arrow_enemies

Merlin or Vertigo

Merlyn I think.

Merlyn

@ms__omega said:

I havne't read many Green Arrow comic but from what I've seen Deadshot isn't even listed as one of his villains. Kinda surprising since the two seem like they would be great paired up against each other.

I'm pretty sure it's Komodo now.

Vertigo.

Beata

After almost a year, I'll update my answer:

DC editorial.

Vertigo is pretty good, but I'm gonna say Merlyn

I think it's a toss up between Vertigo or Merlyn, but I wouldn't discount Deathstroke either. I also great potential for Komodo as well.