Symbolism, Imagery, Allegory
Siblings always share stuff—parents, germs, toys—but the Fitzgerald boys share something kind of unusual: They all have the same middle name. It's Dennis. If you're thinking they must be named after a dearly departed grandfather or great uncle, though, think again:
My brothers and I always called each other by our initials because that was the way Papa addressed us. We all had the same middle name of Dennis, just like Papa. More than two hundred years before I was born, an ancestor of ours named Dennis betrayed six of his cousins to the English during the rebellion in County Meath, Ireland. His father decreed that all male Fitzgeralds must bear the middle name of Dennis to remind them of the cowardice of his son. (1.23)
It seems like a strange thing to want to commemorate, but apparently it works, because none of the boys are cowards. If anything, they love proving how not cowardly they are by beating up other kids in town (though, to be honest, we could see Tom betraying his cousins if the English offered him a penny a head). Additionally, in its unusualness, this shared middle name sets readers up to expect this family to have some quirks to it—enter, the Great Brain.