These guys and gal are NPCs in Borderlands 2.
Borderlands 2 is opening the option to let players customize their favorite guns with decals and enhancements to increase weapon power. Players have to save up a new type of currency called Eridium in order to purchase upgrades and getting ahold of Pandora's best guns.
Just to make things a little easier for everyone, weapon manufacturers will each have their own distinctive gun designs in Borderlands 2. This means you'll be able to better identify guns from a certain maker just by looking at the weapon. Also, bandits now have their own brand of weapons.
Another change coming to Borderlands 2 is having four new playable characters to choose from, one of which was revealed when the game was first announced. The burly-looking dwarf seen on the Game Informer cover is named Salvador, a Gunzerker who has the unique ability to dual-wield guns. One other ability Gunzerkers can learn is increasing the firing rate of their guns over time by continuously holding down the trigger. Class mods, artifacts, and skill trees are also making a return.
Co-op is still locked to four players in Borderlands 2. Moving around the landscape as a team should be easier thanks to new vehicle types and every ride having four seats to accommodate every member.
As for the four Vault Hunters from the first Borderlands, they're still around though only as support NPCs. NPCs in Borderlands 2 will be move lively now since they interact with the environment instead of just standing around in one place.
Update: If you're wondering about when Borderlands 2 takes place, it's set five years after the events in Borderlands. Some jerk by the name of Handsome Jack has not only taken over the Hyperion corporation and declares himself dictator of Pandora, Jack has the gall to claim he was responsible for opening the Vault and eliminating The Destroyer. Jack has also blotted out much of the light on the planet by having a giant orbiting H-shaped base set in front of Pandora's stationary moon. The new team in Borderlands 2 is tasked with killing Jack and returning peace to Pandora.
While the original Vault Hunters are still present, you won't find them hanging out together. They've gone their separate ways to their own part of the planet and still have a bounty on their heads. Finding one of the Vault Hunters is one of your first missions and you'll learn the backstories of each Hunter throughout the course of the game.
Enemies are not just tougher this time, they're also smarter and more dangerous. For starters, partner foes will communicate with each other to change their tactic. You'll also have to deal with elemental Skags who are capable of buffing nearby Skags. Definitely make it a priority to land a headshot or at least quickly land some critical hits when you find this breed of Skag.
There's a chance that players might pick up one of Borderland 2's more unusual guns. For example, Tediore created a gun that's capable of exploding when thrown (more bullets in the magazine increase explosion radius). The gun will then respawn in the player's hands with a new magazine.
Finally, Claptraps are making a return in Borderlands 2. Interestingly, they're putting the blame on Hyperion for what transpired in "Claptrap's New Robot Revolution" and will deal with Hyperion in their own way.