Penguins are most loved and adorable birds in the marine. They are not dangerous to humans but yes, they become aggressive to their counterparts and predators depending on the situation and necessity. Penguins lie between the bird family and the fish family.
In olden days, the penguin was considered to be a fish. Since the loss of flying ability due to their proficiency in swimming, their bones became stronger and they lost the ability to fly and finally, they became flightless birds.