Randy's the oldest guy in the group and basically takes on a big brother role for everyone. He carries a stun halberd in combat and has a natural affinity for Fire magic. Before joining up with the police force, he was with the Crossbell State Guardian Force, but things fell apart after he got into it with the top brass—enough to get him discharged. Sonya Balz, the second in command, vouched for him when the newly formed Special Support Section needed members, and that's how he ended up in the police.
He's protective of the group, but especially looks after Lloyd, filling the gap left by Lloyd's older brother Guy, who's dead. There's clearly more to Randy than he lets on; his background gets peeled back gradually throughout the story, with the full picture finally emerging in the sequel.
Content compiled by AnimeList.moe from publicly available sources.