AC4 is a hardcore band from Umeå, Sweden. Refused members Dennis Lyxzén and David Sandström had been talking about starting a new band for a long time. In the spring of 2008 Karl Backman had written songs for the new band and they started to rehearse. Jens Nordén had played with Lyxzén in pre-Refused straight edge hardcore band Step Forward (1987-1991) and since 1990 with Backman in punk band The Vectors.