The Traveler is what terraformed the other planets as to make them habitable for humanity, and its journey ends above Earth. We know this from the exclusive video shown at E3, in which it depicts the Traveler moving through the Solar System, terraforming each planet as it passes them.

Based on my observations I think the Hive are a race of necromancers who are able to control the bodies of dead humans, Cabal, Fallen, etc. They probably can't control the Vex because they aren't organic creatures. The Necromancers seem to have direct control of their minions, sort of like the Gravemind did with the Flood. But the Hive does not appear to be a parasite, so they probably use some form of dark space magic and a combination of technology to rip the souls out of the sentient organic life they capture/kill and use them as husks. This is similar to how in Myth Balor and the other fallen lords created an army of the dead to fight the Legion. Many of the Fallen Lords were also necromancers who used terrible and powerful magic. If the Hive necromancers do have direct control over their group of minions, killing the necromancer may kill or stop all the remaining minions because they have no guidance and are no longer bound to their master. Also we don't know how many converted the Hive can control at a given time. http://i.imgur.com/u25xGGJ.jpg If you look at the Hive in this picture, you can see "it" is instructing the dead on what to do. The Hive "necromancer" also strongly resembles as S'pht compiler from Marathon with it's long flowing robes. If you look in the trailer, it is evident that the Hive "modify" the victims they capture, sort of like the Reapers from Mass Effect and the Combine for Half life. They appear to remain mostly organic in nature but are infused with presumably a form of Hive technology and some dark form of space magic to animate their corpses. You can see here: http://www.bungie.net/pubassets/3857/10_1_Hive_5_shot.jpg That some of the victims of the Hive appear to have massive holes missing from the bodies and organs removed. It is not something most creatures (especially humans) could survive from. It was odd that they had that very large alien chained up after he appears to have been captured and transformed to serve the Hive. It could be possible sentient beings being converted by the Hive can resist their control. I doubt races like the Fallen could because their souls escape their bodies at death.

I like your theory and id like to give you mine. I think the traveller wasnt on earth like u said, but it was in our solar system. Bungie said that it "breathed new life" into our solar system. That is why we have jungles on venus and stuff. So the traveller to me is like a sort of terraforming device as well as a magic floating ball. So now i think that humans being so amazed by this, studied the traveller. After years and years they had incredible technological advancement. Now, for the reason why the traveller is here. I think that the traveller was built by humans in the future ( i know it sounds crazy ). Now the humans in the future were probably the last survivors on earth and created the traveller to go back and save humanity. I think the thing that the traveller was trying to face was the pyramid race. This race was so powerful and advanced and was trying to conquer the universe. They had already conquered many solar systems and when they headed for us we couldnt stand a chance. Then the traveller came down and activated a forcefield. It used up so much energy defending us with its force field that it fell apart a little bit. The fifth race knew they couldnt stop us now so they went away. Now the cabal and fallen are coming to our solar system because they know there is living conditions in all the planets and they are afraid of the fifth race. They know about the traveller and its power and they want it for protection against the fifth race. So we are at war with them for the traveller and our old worlds. Now the hive were probably created after the traveller breathed life into our system. However they were hidden away so weve never seen them until now. They are just animalistic creatures that run on pure instinct. Now the vex are like biological creatures that gave up their bodies for robot ones (like you said) and they are very advanced and are just trying to take control of our solar system. Well thats my theory. Im basing it off of extremely little info but this is what i came up with.

[quote]For a while I have been perplexed by the Traveler and what it has done in the Destiny universe. To my astonishment, there have been surprisingly few threads about the Traveler itself. [b][u]BE WARNED, FROM THIS POINT ON MY THEORY GETS A LITTLE BIT CONVOLUTED AND A LOT CRAZY. I BASE ALL OF THIS OFF OF VERY VERY LITTLE INFO[/u][/b] [b]The Arrival:[/b] Bungie has stated that the arrival of the Traveler sparked a golden age in which Humanity finally stretched beyond Earth. However, I am not fully convinced that the Traveler was even at earth when Humanity found it. Why is that? because Bungie stated that "It made its last stand at earth". Why would they say this? I feel that its because it wasnt at earth until it made its "last stand" (I will explain more of that later). Now how did Humanity find the Traveler? My guess is that, chronologically, when Humans found it we were in our current era of technology. My guess is that the Traveler was OUTSIDE of our Solar System when Humanity found it. When Humanity found it, they immediately began to examine it and find out more about it. With the technological advancements gleaned from the little info they could get from it, Humanity immediately began to spread and make the other planets habitable. All the while, the Traveler is still in Interstellar space unmoved and still mysterious. [b]The Conflict:[/b] With the discovery of the Traveler and the advancements Humanity was making with the Traveler, two other beings were also able to find the Traveler. Those two beings would be the Cabal and the Fallen. These two species were drawn to the Sol system like moths to a light because of the Traveler. However, even though they try to access the Traveler they cannot. This is supported by the fact that we have seen no Fallen or Cabal in any footage using "space magic". Now obviously with the presence of three powerful races, Humans, Fallen and Cabal there is going to be a power struggle as these two new alien races obviously want to expand to the Sol system. This sparks a war that lasts quite a long time. The war is taking place on all fronts of the Solar system and is driving Humanity down. I believe that in the later years of this war that it was mostly centered around Earth. To support this, in the E3 footage it shows how Old Russia had a wall built around it. Why is there a wall there and why is it not protected by the Traveler? Because Humanity was losing the war, it was a form of defense from these beings, but Humans were certainly not defeated...not yet. [b]The Cataclysm, and why its called The Traveler:[/b] Now this is where my theory gets pretty crazy. All the while during this war the Traveler is sitting motionless and unresponsive outside of our Solar system...until the war reaches a boiling point. When the war is threatening all life in the Solar system, the Traveler...begins to travel through our Solar system. Why is it traveling through our solar system? To end the war. I think that the Traveler began a form of "warpath" through the solar system indiscriminately destroying nearly all life on all the planets to quell the violence. It was programmed to destroy as much life as possible without making the individual races themselves go extinct. So why are there an abundance of Cabal on Mars and Fallen somewhere else? I think that is because, for example, lets say the Cabal were winning the war on Mars, so the Traveler "let them have Mars" and destroyed the remaining Humans and Fallen on Mars so that the Cabal could have it. And Europa (I think thats where the Fallen have taken residence?) was the same, but with The Fallen being the victors. That is why Humans are currently on Earth and not one of their other worlds, because Humans were winning on Earth and the Traveler "let them have it". The cataclysm in itself was merely the Traveler on a mission to purge out all the violence from the Sol system. And it did this by using its mysterious powers to kill off nearly all life in the System. [b]The Last Stand of the Traveler:[/b] Throughout the Travelers voyage through our System, destroying life, it did not avoid damage. I believe that the scars we see on the Traveler now are from defiant Humans, Fallen, and Cabal trying to stop its warpath. However, I believe it did most of the damage TO ITSELF. It was slowing down because of the damage it was taking, and was unable to move to to Venus and Mercury in time to "purge" them as well. I believe it sent out a destructive wave of energy towards the two planets and buckled under the pressure of its power and cracked open so to speak. That is why it stopped at Earth and with the last of its power, decided to hang low and protect the weakest race, Humans, with a barrier. [b]Why it was sent here[/b] This is where I start to really scratch my head. I believe it has something to do with the race that controls the Black Pyramid ships. I think that this race sent the Traveler as a beacon to show them where life was. I think they have a plan on using the existing life forms in the Solar System for some unknown purpose. [b][u]EPILOGUE: ALSO HIVE AND VEX[/u][/b] Now the reason why Humanity is so calm and happy beneath the Traveler, is because, I think, that throughout the years, the sheer loss of Human life resulted in a massive loss of history. The War and the Travelers wrath takes place throughout hundreds of years, and I belive that throughout this time, the truth about the traveler was simply lost and forgotten. I know what you are thinking, "You have all of these hair brained theories but you have failed to include these two races", well, I have a theory... I have heard talk from forum goers that they believe the Vex come from the future, but I believe that they come form the Past! Why else would bungie design them artistically to look "like battered and hammered bronze" unless they were to appear as if they have withstood the test of time? Vex - I believe that the Vex were part of a formerly biological race that was about to be destroyed by the Traveler. This race decided to give up their bodies for timeless robotic ones, and travel into the future to begin spreading their race again AFTER they believed the Traveler had been dealt with. Hive - this one I am a bit more dumbfounded by. The Hive queens obviously have some form of space magic going on as they seem to float and have a very Supernatural vibe about them. I think that the Queen of the Hive could have been "mutated" by the power of the Traveler and now has some of the powers that the Pyramid race has to alter life. They utilize this power by raising undead armies to try to reclaim some form of lost glory. [b][u]END[/u][/b] I tried to warn you, u wooden lisen. I told you it was going to be crazy! But just how crazy? I believe it was the RIGHT amount of crazy. Like I said, I based nearly all of that off of the tiny bits of info we have on Destiny, and tried to put this grand puzzle together the best way that I could find. please, share with me what you think of my theory.[/quote]. I do have to say very well thought reason. Well I think the travler came to our solar system to discover new life. Like u said the travler came probably along this time in tech but the other races were chasing after it to discover its secrets. That's when all hell broke loose. The travler came to earth to save us because we were a young race. It sacrificed all of its essential life to help save us. It saved us on earth because it was our home planet. Now it's power is making a magical barrier to keep evil out of the city.

One or two things, we didn't find the traveler the traveler found us, and as to bringing new life into the universe it teraformed (made habitable) all the other planets allowing us to live on other planets and fine their secrets it also helped further develop our technology etc. blah blah as for everything else idk