Steve Murphy is sort of like the male equivalent of Tina—and, in fact, he's dating her. Steve is loud, obnoxious, and at the top of the food chain. Park thinks Steve "looked like a grown man since the seventh grade, and that was before he grew a full beard" (1.15). He's a drinker and pot smoker, and almost everything he says is either stupid or offensive.
Even though Park's known Steve forever, he's not a fan. Steve's the one who often leads the rounds of chanting and catcalling on the bus; Eleanor describes Steve as "standing at the back of the aisle, waving his gorilla arms like a conductor" (22.28). When Park finally loses it after a chant directed at Eleanor, he nails Steve with a flying kick.
Like Tina, Steve does come through in the end and helps Eleanor find Park when Richie's on the warpath. He might be a bad kid, but he's not evil like Richie.