The blue whale is a “rorqual”, a member of the family of whales that includes the minke whale, sei whale, gray whale, and humpback whale.
The only animals, other than humans, known to pose a threat to blues are orcas. The blue whale’s massive size scares off most predators, and it can deliver a powerful slap with its giant tail.
Blue whales were hunted by human whalers beginning in the 1930s, when new harpoon developments made them a more viable target. Since 1966, hunting blue whales has been banned worldwide, though certain countries continued to hunt them illegally into the 1970s.
Blue whales are mentioned in Herman Melville’s famous novel Moby Dick, where they are called “sulphur bottoms”. This name refers to algae called diatoms which are known to accumulate on blue whales’ undersides, giving them a yellowish hue.