This Hungarian literary historian with the seemingly unpronounceable name (something like Jerj LOO-kach) had a long run as an intellectual and aesthetician, but he was best known as a Marxist philosopher.
Lukács liked to change his mind a lot and argue with every other Marxist he came across, but he is credited with establishing Western Marxism, and he spent a good chunk of his life thinking, breathing, defending, and revising his opinions about Marxism. During one of the less savory periods of his life, he was involved with Stalinism, a particularly extreme form of Marxism named after that maniacal dictator Joseph Stalin—but his interest in it didn't last.
Unlike Derrida, who is surely known and discussed in everyone's home, Lukács isn't quite a household name—but he was wildly influential for his fellow critics. Before he got into Marxism, he concocted an aesthetic theory that, among other things, condemned Modernism and totally defended Realism and the realist novel. Lukács instantly consigned any novel that was narrated through the perspective of one wildly subjective protagonist to doorstop status.
Like any good Marxist, Lukács was concerned with all the people. He didn't want novels about one person's petty problems; he wanted novels that explored big social, political, and economic issues.
He also focused on some of the nitty gritty issues in Marxism, such as the alienation of people in a capitalist society, the class struggle, and other pet subjects. In fact, he was a bit of a purist, and he didn't like the way other schools of thought (like psychoanalysis and structuralism) were trespassing on Marxist territory.
Lukács wrote many of the basic works of Western Marxism, including the much loved Theory of the Novel (1916) and History and Class Consciousness: Studies in Marxist Dialectics (1923), but one of his biggest barn-burners was a little thing called "Reification and the Consciousness of the Proletariat," which points a sharp bony finger at how the cultural obsession with producing commodities infects life as we know it.
"Reification," as he called it, meant that people were becoming detached from their own abilities and qualities, and everything and everyone was being transformed into a consumable object. Our contemporary fixation with "branding" ourselves is just an extreme version of the way we participate in own commodification. Reification as extreme sport, anyone?
Thank goodness ol' Lukács isn't around to see capitalism gone wild.