A big mass of something that looks like grape jelly, the Blob is a fast moving fleshy pink/purple coloured shapeless organic plasmic lifeform, which travels by slithering. It can fit into any space and has an unquenchable hunger for anything organic, mainly animal lifeforms. It grows as it devours and is generally incapable of higher thought. Gelatinous, translucent and "goopy" in consistency, sliding, and pouring along the ground. it has no skeletal system and can squeeze through nearly any gap and can change it's shape almost at will. It is able to form tentacles or tendrils which it shoots out to grab hold of its prey, and is surprisingly strong, enabling it to crawl up walls, support its entire weight (and that of its prey) while clinging to the ceiling, bend metal doors, or pull an entire adult human through a gap the size of a plug hole. When the Blob seizes its prey, it envelopes them completely, secreting an acidic enzyme which quickly melts the prey's skin and dissolves its flesh. Sometime the Blob will kill its prey and then slither inside the corpse, waiting to ambush anyone who comes close enough. Though the Blob can survive underwater for long periods of time (possibly indefinitely), and does not appear to require oxygen or air (as it was developed under vacuum conditions in space), it cannot stand cold temperatures. Extreme cold will cause the Blob to become crystalline in nature, rendering it useless, though it may be able to survive if the temperature is raised. It can possibly be similarly dehydrated by high temperature.
On its first recorded 1958 appearance, the Blob arrived on Earth by accident on a meteor. The 1988 occurance was created, based on research on the original blob, as an experimental virus by the US Army to be used for biological warfare and started life as simple bacteria launched into orbit inside a specially built satellite to be exposed to the conditions of space and mutate. Growing fast, its mass would have thrown the satellite off orbit and towards Earth. When the satellite crash landed, the mutated bacteria, or Blob, was able to escape and wreak havoc.
Source: The Blob (1958), Son of the Blob / Beware the Blob (1972), The Blob (1988)