Blasters were zombies created by the nuclear missiles launched as a result of Murphy breaking quarantine at the CDC lab in Fort Collins. They were humans killed in the blasts and the radiation made them significantly different from regular zombies.
It was also stated that those who were killed by the fallout radiation became blasters, however if this was true it must either have required a particularly high dose or the transformation was not instantaneous, as several people slowly dying of radiation sickness did not appear to be blasters upon reanimation. It is unclear why blasters manifested differently from the radioactive zombies.
Blasters were mostly bald and had very pale skin marked by deep red patches (possibly either burns or dried blood). Most of their ragged clothing appeared a bleached white.
Blasters retained a higher level of intelligence than most zombies. Unlike others, they would retreat or use cover when injured or surprised. They were capable of planning ambushes and shared a sort of pack mentality, hunting in groups with an apparent hierarchy. Some were even seen utilizing a barricade (though it was unknown if they themselves built it) and wielding torches. They had the advantage of being significantly faster than other zombies (easily able to keep pace with speeding cars and jump on with a little effort), and could move with surprising stealth. This combination allowed them to surprise and kill their human prey before they even realized they were in danger. Unlike normal zombies, they would kill all the humans in a given group before eating, and when they did they only ate the brains, not all flesh. This usually resulted in their victims being left with all the flesh ripped off their faces but otherwise showing no other injuries.
The Blasters were highly resistant to Murphy's telepathic ability to control other zombies. When they came close, he began to hear a sharp static-like sound, and upon attempting to control the Blasters he was shown to be physically pained by the attempt. He struggled immensely to keep three of them at bay for a few seconds, and when the "alpha" of their pack appeared to support them, Murphy's ability was overwhelmed. The blasters clearly disliked his attempts and became even more aggressive towards him in particular. However, Murphy was able to control a single blaster in "The Collector" with no apparent issue. While it was suggested that the radiation may have melted their brains, making it impossible for Murphy to control something that isn't there, no proven explanation was given for this resistance. However, Murphy only had varying degrees of control over zombies beyond the standard kind (another example being the phytozombies), so it's possible they simply weren't similar enough to him to be completely controlled.