"Avengers 3" will signal the end of Marvel's Phase 3. Expectations are high and it will probably feature a grand battle royale similar to the Infinity Gauntlet. This is the direction that they have building at right from the start.

One of the principal characters of the Infinity Gauntlet is Adam Warlock-whom we might have already seen in one of the movies.

From What Culture: "Adam Warlock is undoubtedly the key character (other than Thanos himself) in the Infinity Gauntlet comic book arc and it's absolutely essential that he appears when the movie portrayal is made.

Warlock acts as the heroes' guide when it comes to defeating Thanos, having been newly resurrected following his previous demise. At the end of Thor: The Dark World, in the mid-credits scene when the Collector came to Asgard to pick up the Aether, a cocoon can be seen that is very similar to the one that Warlock emerges from. If, as expected, it turns out to be Warlock himself, he could emerge from it for that very same reason when Thanos gets his hands on the Infinity Gauntlet in the Marvel Cinematic Universe."

Marvel has actually placed the character on hold in the comics. Jim Starlin, writer and creator of the Adam Warlock character lamented on Facebook:

"Okay, this time, after I brought Adam Warlock back from the dead in The Infinity Revelation, someone at Marvel anonymously put a corporation-wide-no-use restriction on the character, effectively putting the brakes on the ongoing plans I had for him and [Thanos]," Starlin wrote.

"When I started on The Infinity Revelation, I asked about Adam's status, was told no one had any plans for him and that he was dead. So I brought him back to life in the graphic novel and made plans to use him further.
I turned in a plot to Tom Brevoort, which included Adam Warlock, and about two months later Tom informed me about the hold but said he couldn't explain it to me. That's when I took on the Savage Hulk story arc, to keep busy until the hold was lifted and built up some more advanced storyline for the proposed project (The Infinity Duel). The hold is still in place and, apparently, shows no signs of being lifted any time in the future. So I'm moving on."

Why would Marvel hold the story of Adam Warlock? It is commonly presumed that such a move is necessary so that the Cinematic representation would not be left behind by the comics. The key is that both media would spark interest in each other.

The role of Adam Warlock, who is Thanos' ultimate nemesis, is definitely an integral one. It would be very intriguing to know which actor Marvel will choose.

In the meantime, "Avengers: Age Of Ultron" will be shown on May 1, 2015.