All righty, here's my elaborate (but probably wrong) theory on just who Harrison Wells really is. I'm more than convinced now that he is, in fact, an older, future version of Barry Allen. After all, I think it's more than coincidental that the actors playing Barry and Wells (Grant Gustin and Tom Cavanaugh respectively) have uncannily similar builds, but are both dark haired and blue eyed. Moreover, I believe Wells is the future Barry Allen from the original timeline. Why do I say that?
Because thanks to "the man in the lightning" killing Barry's mom, history has already changed.
I think the "backstory" for this show is as follows: in the original timeline, Barry Allen becomes the Flash as we've seen except for one crucial difference--his mother is still alive, which means Barry's dad never went to prison, just like the pre-Infinite Crisis comics. Also, in this timeline, Barry and Iris would go on to have a romantic relationship and get married, again just like the comics. However, ten years from now, Professor Zoom, in order to get revenge on Barry, killed Iris--which, by the way, was a classic storyline from the Silver Age Flash comics.
But Zoom wasn't done. Zoom goes back in time to change history by killing Barry's mom, and Barry, i.e. Future Flash, managed to chase after him to try on stop him, but couldn't save her. Notice how, in the pilot episode there are actually two streaks circling around Barry's mom? One of them is yellow, which is Professor Zoom, and the other is red, which is characteristic of Barry. This also explains why the young Barry was suddenly transported outside at super speed--Future Flash was forced to save his younger self at the cost of his mom. This also explains how the Flash, ten years from now, disappeared.
Knowing that history had now changed and that he couldn't go back to his original time, Future Flash decided to stay in the past in order to ensure that his younger self still became the Flash and set things right as much as he could. Using his knowledge of the future and scientific advancements, Future Flash changed his identity to Harrison Wells, founded STAR labs, recruited up and coming scientific talents like Caitlin and Cisco knowing they would provide an ideal support network, and built the particle accelerator knowing full well that the accident would result in his younger self gaining superpowers.
As to why Wells is willing to kill which doesn't at all seem like something Barry would ever do? Consider this: if Wells is indeed a future version of the Flash, then not only has he witnessed the murder of his wife, but also his mom, and his entire future. That would obviously unhinge even the most sane of people, and would also make someone go to extreme lengths to protect others, including himself.
Notice also that this theory fits in terms of the character's ages. Barry, as we know, is currently 25 years old. His mom was murdered when he was 11, i.e. 14 years ago. Future Flash, ten years from now when he disappeared, would be 35. If Future Flash went back in time 14 years ago from 2024 to 2000 and stayed in the past, aging normally, then today, Future Flash would be around 50--which is the same age as the actor playing Harrison Wells.
As for Professor Zoom, that's clearly Eddie Thawne (again, just like the comics), and I believe his joining the Central City police force and dating Iris is purely calculated. Why? Again, his getting Iris to fall in love with him is yet another way to get revenge on Barry and to alter his future without erasing Barry from history and thus jeopardizing his own existence. Yeah, Eddie seems like a nice guy, but superficially so--just enough to convince audiences that, while a rival for Iris' affections, he's doesn't seem like such a bad guy, even to Barry.
