This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Og (Jewish)
Og according to the Hebrew Bible and other sources, was an Amorite king of Bashan who was slain along with his army by Moses and his men at the battle of Edrei. Og was one of the giants of the remnant of the Rephaim. His iron bedstead in Rabbath, the capital of Ammon, is described as having been nine cubits in length and four cubits in breadth.
Og was not destroyed at the time of the Flood, for, according to one legend, the waters reached only to his ankles. Another tradition states that he fled to Palestine, where there was no flood while, according to a third legend, he sat on a rung of the ladder outside the ark, and, after he had sworn to be a slave to Noah and his children, received his food each day through a hole made in the side of the ark.