What does Blackie symbolize in "The Destructors" by Graham Greene?

Blackie symbolizes the more typical boys' gang leader of the early part of the twentieth century. Like the other boys who join together in mischievous conduct for thrills and a sense of camaraderie and belonging, Blackie is one of the group, and is a friend of the other boys. The acts that he and the others commit are emotionally driven whereas Trevor--T. as he is called because he has an upper class name--are simply acts of nihilism, symptomatic of the psyche of many a Londoner after the destruction of World War II.

"All this hate and love," he [T.] said, "it's soft, it's hooey. There's only things, Blackie," and he looked round the room crowded with the unfamiliar shadows of half things, broken things, former things....

Whereas T. perceives destroying Old Misery's house as a creative act (for which he exploits others in his design) since it is performed craftily so that it does not collapse until nothing inside is left, Blackie and his gang have entered Old Misery's home before and committed single acts of vandalism without stealing any of his money or destroying the house. T. does not want the money either, but he has it burned, again enjoying pure destruction.

The only reason that Blackie joins in the tearing down of Old Misery's house is the fact that he wants to be with the gang and he desires fame for his friends:

Driven by the pure, simple, and altruistic ambition of fame for the gang, Blackie came back to where T. stood in the shadow of Misery's wall.

Thus, Blackie symbolizes a pre-World War II gang leader, a leader in joint vandalism and pranks as acts of bravado and camaraderie. This type of leader is unlike the nihilistic Trevor/T.

Who is the character Blackie in "The Destructors"?

Blackie is the leader of the Wormsley Common gang until Trevor replaces him. Blackie is the one who proposes the gang's daily activities and makes decisions for the group. For example, when Mr. Thomas unexpectedly gives the boys some candies, Blackie is suspicious. He says that he thinks it is a bribe to keep the boys from bouncing balls against Mr. Thomas's garden wall. In order to show Mr. Thomas that "we don't take no bribes," Blackie forces the boys to bounce balls off the wall all morning. Another time, Blackie comes up with the idea to have a contest to see who can steal the most free rides on buses.

It's clear from the outset that Trevor has a different vision for the gang than Blackie. Unlike Blackie, Trevor is uninterested in being the leader, but he is from a higher social class—though his family's position has recently fallen—and his understanding that Mr. Thomas's house is an important architectural landmark is beyond Blackie and the other boys, and he knows he will need their help to achieve his goal of demolishing the house. Trevor's proposal goes far beyond anything Blackie could imagine; once the gang accepts Trevor's plan, Trevor effectively replaces Blackie as the leader of the group.