FBI Special Agent Henry Knox was a recurring character on Beauty & the Beast. He was portrayed by Anthony Ruivivar.
Agent Knox first appears after kidnapping Catherine Chandler from her home. He claims it was necessary, because the police surrounded her place, hoping to find Vincent Keller, who is wanted for murder and is a fugitive after escaping prison. He tells Catherine he wants her & Vincent's help to find Agent Karen Mallory, who was abducted by the terrorist cell she was following. Catherine doesn't believe him until Knox reveals that Dana Landon pointed him towards Catherine & Vincent, saying they were his best option to find Agent Mallory. He says he's willing to get Vincent exonerated if they can help him out. Catherine knocks him and his partner out, and escapes after Vincent tracks her down.
Vincent & Catherine later come back to Agent Knox, saying they're willing to help out. Vincent & Catherine are able to rescue Agent Mallory, and avoid getting caught. However, when they come back, Agent Knox reveals that someone blocked his exoneration attempt. Catherine figures out it was actually Gabriel Lowan, her ex-boyfriend trying to capture Vincent.
Vincent & Catherine see Agent Knox again when they need to hide out. He offers to put them in witness relocation so they can lay low while he works to get the exoneration pushed through. This plan doesn't work out, though, and Vincent & Catherine come back to the city, hiding out in a hostel in disguise. Agent Knox later meets them and says Vincent will get exonerated if he turns himself in. Vincent agrees, and Knox sets up a press conference to let the public know that Vincent has surrendered.
During the conference, a reporter, Beth Bowman, speaks up and asks if Vincent was part of a failed military experiment that super-charged his DNA and turned him into a beast. Knox quickly shuts down the press conference, and dismisses Beth's question as speculation. After the conference, though, Vincent admits to Knox that what Beth said was true in order to protect Catherine from Gabe, who they realize was Beth's source. Knox is furious, but agrees to help them when they promise to keep a lid on the story.
Knox later calls Catherine, and says that Vincent has disappeared from his cell again, having seemingly escaped. In reality, two agents took Vincent out of his cell, claiming Knox sent them. However, Vincent convinces them to let him go. Knox later calls Vincent, and says he's been exonerated of the charges by the agents. When Knox & Vincent go to find them, they've disappeared, and Vincent tells Knox they took a sample of his DNA before leaving.
After Vincent is exonerated, Gabe turns himself into a beast, becoming obsessively intent on hunting down Vincent. In order to goad Vincent to come after him, Gabe brutally kills Agent Knox.