Hades with Cerberus via Wikipedia
Gods are immortal and have particular domains that They control/embody/personify. Demi-gods, or heros, are descended from god and mortal pairings. Demi-gods have abilities that surpass mortals, can cross domains that gods can not cross (like descending into Hades – something we don’t see any gods but the Chthonic gods do, because it isn’t Their realm [except for Hermes and Iris because They are messenger gods]). Yet mortals don’t have the power of gods and can be subject to the whims of gods. Mortals often have a special relationship with their parent god and sometimes are blessed with long life or immortality by their parent god or gods in general. Sometimes they have/had cult worship as well (as in, people pray[ed] to them in addition to the gods).
IMHO, Catholocism adapted the practice of worshiping demi-gods/heros to the worship of their saints (not the same figures in mythology/history, but rather, the very human tendency to elevate certain notable individuals to cult status and ascribing a divine quality to them).
What do you think a demi god is? What do you think defines a god?
Helleneste kai Grammateus 
There are no gods my dear…it’s all mythical.
Hi Alexandrabond, of course the Christian church is mostly Pagan in ritual, although forgotten are the meanings of the rituals.
Isn’t Jesus a Demi-god? The fact is that Christianity looks nothing like Judaism so what does it look like?
My response to this comment is too long for the comments section, I am going to devote a blog post to this. Please check back soon… ; )
I thought I might have opened a door to a store room of your expertise. Look forward to your post. bdrex
What about Dionysos? Can we say he’s the only God who came from a god and mortal pairing? 🙂
Dionisos is one of such cases, but there’s also Asklepios – son of Apollo and Coronis.
so is there a group called Messenger gods? Is Iris a god of demi god?
Hi Carmen,
For the purposes of categorizing the gods in terms of their realms, yes, there are certain gods who can cross boundaries and a few of them do so for the purposes of delivering messages. These include Hermes, Iris, and Hekate.
Hermes serves many purposes – he is a psychopomp (guides deceased mortals to Hades), delivers messages between various beings, brings human offerings to the gods, etc.
Iris was known as Hera’s messenger in the Homeric era. Even humans can see her cross the boundary between sky and earth (a rainbow). She is recognized as a goddess. Her parents are Thaumas, who personifies the wonders of the sea, and Electra (Cloud-Nymphe) of the amber-trim, storm-clouds illuminated by the returning sun. For more information on Iris, see: http://www.theoi.com/Pontios/Iris.html
Hekate is the goddess of doorways crossroads (among other things). Her images and altars appeared before private homes and city gates. While she is a goddess of transitions, she is not a “messenger goddess” per se, but does act as a guide.
When u looks critically to the situation in the world, you should be able to know that demi god exist