Ecne was a Celtic god. He was one of the Tuatha de Danann and the god of wisdom/knowledge.
It is unknown what Ecne looks like. I couldn’t find this information written or in an image.
According to Celtic lore, Ecne was the son of three brothers, each his father: Brian, Iuchar, and Iucharba. These three brothers were the sons of the goddess Brighid and god Tuireann. There is some debate, however, about whether the three brothers were born of Brighid or another goddess, Danand, who was the daughter of Tuireann. Regardless, their father seems set to be Tuireann. The three sons are often considered to be the three gods of dan, or knowledge. Thus Ecne is the son of knowledge.
Ecne’s fathers are also notable because they killed Cian, the father of Lugh.
Unfortunately, Ecne does not appear to have his own myths that would tell us what his personality is supposed to be like.
Light and Dark Sides
Because Ecne has no legends of his own, nor does he seem to be a player in other myths, we don’t know what his Light or Dark sides are like. We can only guess that he would be a Light deity since he is a god of wisdom, and in general wisdom is placed on the Light side of the scale. Wisdom itself is neither good nor bad, but a tool, so lacking any further information we could say Ecne is a neutral deity, which may be closer to his personality anyway.