Yakkha is often translated as “Giant”.
But I remember in Culasaccaka Sutta, Vajirapani (aka Sakka) is known as “Yakkha”.
Since Sakka Devaraja is Deva , how come he be a Yakkha at the same time? So can it be Deva = Yakkha?
Or Yakkha is just a designation for supernatural being?
Vajirapani Yakkha prepared to strike down Saccaka
Theravada (Thai) tradition of Yakkha
It is often translated as giant but ogre is probably a better translation. Yes it is a supernatural being and you can be a deva yakka up to Catumaharajika. The nagas, yakkas, kumbhandas and ghandharvas can also be devas up to catumaharajika, meaning they can be devas up to 1st level as well as earth devas (bhummadevas). For devas above catumaharajika they can only be “human” devas.
So in short, devas from level one and below can be of human, nagas, yakkas, kumbhandas or ghandharva form. But from Tavatimsa and above all the devas are of human form.
Yakkas who are also devas that you see in the texts are simply devas with a yakka form rather than a human form.
Yakka is also mentioned as amanusa (not human, that lusts for human flesh). Ogre is defined as a giant that eats human flesh.
Ogre - An ogre (feminine: ogress) is a legendary monster usually depicted as a large, hideous, man-like being that eats ordinary human beings, especially infants …
See Alavaka Sutta
Jataka story: Prince Five-Weapons and Sticky-Hair (The Diamond Weapon)
Another story is about an ogress, who lived among houses of people, searching for food. They have to eat human urine, mucus, etc. despite they are a type of earth-dwelling deva. The ogress had a baby, crying because it was hungry. She ignored him, as she also heard the monks reciting the Dhamma. She did not understand the meanings, but she paid attention to the voices of the monk and eventually attained sotapanna fruition.
Another story is a woman and ogress - the ogress pursued the woman for her baby. The lady found her way to Jetavana Monastery, when the Buddha was residing there. See this Verse 291
Many types of ogres - some are deva, some are half-peta, but all of them seem to belong among Catumaharajika Deva, at different levels, have sufficient intelligence and capable of understanding the Dhamma.