Susannah Tyler

In a dream world created inside Rose Tyler's mind while an entity devoured her, Susannah Tyler was Rose's daughter. In the dream, a version of the Ninth Doctor appeared too late to take Rose with her as she already had a daughter, so instead the Doctor kidnapped Susannah and made her his new companion. The Doctor returned to Rose to invite her again, stating that she was either married to an alien guard or stayed behind on a planet to lead a rebel group, but Rose refused, and eventually saw through the dream. (COMIC: The Cruel Sea)

Behind the scenes
The father of Susannah is implied to be Mickey Smith. Rose is pointing at a "stupid lump" she needed to take care of, corresponding with a similar (but longer) scene in the television story Rose, followed by a montage consisting of a wedding photo, which is later broken, and Rose taking care of Susannah alone. Susannah also has a similar skin tone and hair texture to Mickey. Mickey is not directly glimpsed in the Rose flashback in The Cruel Sea, but his presence is implied, with the features of the "lump" hugging at Rose being obscured by Rose's arm, and in other panels he is either out of frame or seen from behind. The shattered wedding photo also obscures the husband's features.