Gabriel Waincroft (Christopher Sean) is the younger brother of Malia Waincroft, the late wife of Chin Ho Kelly. As an adolescent he repeatedly got into trouble with the law and Malia went to Chin, then her boyfriend, for help in setting him straight. Gabriel was initiated into a gang after killing Chin 's father and rose through the ranks of the (fictional) Culiacan cartel based in Sinaloa, Mexico. With Wo Fat 's death, Waincroft is now the team 's primary antagonist. He has been described as daring and ambitious, particularly after he had his men attempt to assassinate the heads of three different criminal syndicates during a high - profile boxing match (the attempt was discreetly foiled by Five - 0), in the episode "Ka Makau kaa kaua / The Sweet Science ''. In "Pa'a Ka ' ipuka I Ka ' Upena Nananana '', he was badly wounded and died in surgery from cardiac arrest. His daughter Sarah is currently being cared for by Chin as her legal guardian.
who plays chin ho kelly's brother in law
Christopher Sean