The Blackbeard Rum branding was done by Germany-based design agency Pixelinme, and takes its ideas from the notion of pirates in the Caribbean (not necessarily the movie, but the literal fact that these people used to cause ruckus in this part of the world).
An octopus seems to be a common element running throughout the branding process here, as certain photos feature a tentacled arm running over the bottle. While an octopus is not present on the bottles, curved lines similar to the outline of this creature are drawn on the front. The designers went with an all-black look to give the bottle a look of sophistication and class. The Blackbeard rum brand wanted to promote a sense of exclusivity with this design.