"...a figment of what might have been."
- - Captain Kathryn Janeway, 2380
Eddie was born after his parents married as they had intended, in the normal real timeline this had not been possible because Justin Tighe had perished in an accident at Tau Ceti Prime. He lived on the USS Voyager with his parents, his father being the captain and his mother the first officer.
When his mother returned from her encounter with the Guardian of Forever she had no real memory of him, and spent several hours playing with him, without even knowing his name.
Eddie enjoyed playing with action figures and drawing. Some of his favorite foods included macaroni and cheese and hot dogs, he chose both dishes to eat when his mother allowed him to choose, which until then had been something he had rarely if ever been allowed to do.
Though Eddie showed a great talent and affinity towards arts and design his parents both steadfastly forced Eddie to focus on science. This was because in this timeline Janeway had never reconciled and bonded with her sister Phoebe over the death of their father. Janeway remained dismissive of arts and did not like her son sharing any such interest. Justin agreed and both always discouraged Eddie from pursuing arts of any kind.
After returning from the Guardian of Forever Janeway temporarily retained her memories of the previous timeline. She recognized that her and Justin forcing Eddie to focus on sciences was hurting the boy. Eddie was often treated harshly by his father, who became angry when his son acted like a child or strayed from the ideals he had laid out for the boy. She attempted to rectify all this and argued with Justin to do the same.
After breaking orbit from the Forever World Janeway attempted to avoid Tighe as much as she could and spent a great deal of time with Eddie. She became completely smitten with him and thought of him as the cleverest and funny boy she had ever met. Eddie enjoyed spending time with his mother, and telling her stories of all kind. Something she never had any interest in before.
Eddie Tighe ceased to exist when Seven of Nine returned the timeline to its normal and intended path. His loss was a source of great pain for Janeway and made Seven feels extremely guilty. Janeway did however point out that Eddie had in fact never really existed, only as a glimpse of what might have been.
Janeway and Seven indicated that when they had a son of their own they intended to call him 'Eddie' in honor of Eddie Tighe.
Eddie is most likely named after Edward Janeway, Katryn's late father, though this is never confirmed.