A Picture of my 3x Greatgrandfather

This is my great-great-great-grandfather, Martin Gillan:

(I want to say he's the family patriarch, from whom are descended all of the Gillans I've encountered since I started doing research, but that's not entirely accurate. I was once contacted by a descendant of his brother, so really, I have to find Martin's parents - my 4x great-grandparents - to find the ancestors from whom we all descend.) 

A few months ago, I was contacted by a second cousin thrice removed who sent me this photograph of his great-grandfather, my 3x great-grandfather Martin Gillan. He was born c. 1825, but lived, according to his obituary, an astounding 104 years, and died in 1929, which is why I'm lucky enough to have a photograph of him. 

My cousin told me that it was a photograph of "Daddy Moore," which left me a little nervous that we had a case of misidentification. I forwarded the picture to our mutual cousin Mary, who never knew Martin Gillan but grew up in the same town he had lived in and knew a little more about him. Probably sounding like an American boob who wouldn't recognize a word of Irish if it bit me on the nose, I asked her about the name "Daddy Moore." Why would they be calling this guy Moore if his name is Gillan? Patiently, Mary explained to me that Martin Gillan was known by his many grandchildren as Dada Mór, Irish for Granddad. A great family picture and an Irish language lesson all at once - now that's a success!