He was the true leader of the semi-titular Spiders that acted as the supporting antagonists - he also had a mate in the form of the Queen Spider, but it was the "General Spider" that took the role of the main protector for the Spiders as well as the one responsible for the abnormally aggressive and dangerous actions the swarm took in regards to humanity.
The "General Spider" was much larger than the other Spiders (rivalled only by the Queen) and was also the most intelligent and arguably the most malicious of the swarm as he was actively seeking to murder those that got in his way (though it was likely for what he saw was the survival of his offspring).
In the climax of the film, the "General Spider" engages in a combative fight with the film's hero after he has the swarm attack the hero's home - which was the site of one of his nests, guarded by the Queen - who the hero killed via electrocution.
This angered the "General Spider" and as the hero tried to set fire to the nest the "General Spider" confronted him and a deadly game of cat and mouse ensues in which the "General Spider" shows his remarkable intelligence as he repeatedly evades attempts by the hero to kill him with a homemade flamethrower and comes within inches of killing him on several occasions.
Finally after the battle results in the hero toppling over and becoming trapped the "General Spider" climbs up slowly, showing that he was aware of the hero's fear and played on it (as he could have bitten the hero's foot or leg had he simply wished to kill him outright) - yet this proved the fatal mistake of the "General Spider" as it climbed towards the hero's face only to walk on a small piece of wood that the hero flicked over, causing the "General Spider" to fly into a nearby fire caused by their previous battle and gets ignited.
Yet in a final fit of rage the dying "General Spider" raced towards the hero (while still on fire) determined not to let him leave the basement alive - only to be killed by a nailgun that also fired his flaming corpse into the nest, killing the emerging offspring as well, the ovicidal hero promptly saved from the ensuing inferno by an exterminator (who had killed the swarm that had invaded the house above).