Just like the first three seasons of "Arrow," Oliver Queen will face off with another powerful adversary when the show kicks off Season 4 this October.

In Season 1, Oliver went head-to-head with Malcolm Merlyn. He then endured an ongoing battle with Slade Wilson, who is also known as Deathstroke, in Season 2. During the Season 3 finale, the vigilante finally defeated the all-powerful Ra's al Ghul before retiring and driving off into the sunset with Felicity.

Although the season finale ended on a good note, it won't be long before Oliver will have to return to Starling City to face a new big bad that may be even more intimidating that Ra's al Ghul. According to Comicbook.com, two leaked video transcripts revealed that "Arrow" producers held a casting call for a new villain named "Simon," which may be an alias or a pseudonym for DC Comic villain Damien Darhk.

In one scene, Simon mentions to Oliver that he had a past connection with Ra's al Ghul. At another point, Simon says that Ra's feared him, and that he is more dangerous than both Merlyn and Slade.

Another scene features Simon admitting that he once felt vulnerable and at the mercy of someone else. However, he dealt with his vulnerability by cutting off his emotional ties to other people so that he would no longer feel threatened or fear. Both scenes hint that Simon is actually Damien Darhk, Ra's al Ghul's former ally in the League of Assassins.

Back in Season 3's episode "Al Sah-him," Ra's told Oliver about how Darhk believed he should be the one leading the League, but was angered when Ra's was chosen instead. Ra's was ordered to kill Darhk, but he hesitated, giving Darhk the opportunity to escape with his followers, their secrets, and some water from the Lazarus Pit, reports Den of Geek. Darhk then went on to form his own organization, H.I.V.E., which is known for being super high tech.

H.I.V.E. was first mentioned on the show in Season 2 when it was revealed that the organization hired Deadshot to kill John Diggle's brother Andy.

Actor David Ramsey, who plays John Diggle, also teased that H.I.V.E. will have a major role in the upcoming season.

"From my understanding, H.I.V.E. is going to be a big part of next season's big baddie. ... We are going to delve right into why H.I.V.E. hired Deadshot to kill Andy and what H.I.V.E. is all about to begin with. There will be a lot of Diggle's connection to H.I.V.E. next season so stay tuned," he told E! Online.