A new and distinct primocane-fruiting (autumn-bearing) cultivar of black raspberry, Rubus occidentalis, named 'Explorer.' The 'Explorer' black raspberry was created as an F2 generation seedling of a controlled cross between two unnamed black raspberry plants collected from uncultivated areas. 'Explorer' black raspberry is capable of providing a reliable and productive crop of large black raspberries on primocanes in late summer and early autumn when there are no fresh black raspberries available from other cultivars of black raspberry. The canes of 'Explorer' black raspberry also exhibit fewer thorns than canes of a typical black raspberry plant.