Name Rocky Thermopolis-Gianini
Birthdate Sunday, May 11, 12:01 a.m Eastern Standard Time
Weight at Birth Four pounds, fifteen ounces
Hospital St Vincent's Maternity Ward
Siblings Amelia (Mia) Mignonette Grimaldi Thermopolis Renaldo
Parents Helen Thermopolis and Frank Gianini

Rocky is Mia's little half-brother with an age gap of 15 years. Rocky was also going to be called Sartre. Mia is constantly caring for Rocky and singing him to sleep that she developed the nickname Baby-Licker (BL) from Lilly Moscovitz (later Helen). Rocky was born the night of Mia's prom, so Lilly and Michael Moscovitz came with Mia to the hospital. Her diary entry is as followed:

'Oh . . . my . . . God.

I can't believe it. I really can't. Tonight, not only did I become a woman (maybe) but I also became a big sister.

That's right. At 12:01 a.m., Eastern Standard Time, I became the proud big sister of Rocky Thermopolis-Gianini.

He is six weeks early, so he only weighed four pounds, fifteen ounces. But Rocky, like his namesake - I guess Mom was too weak to argue for Sartre any more. I'm glad. Sartre would have been a lousy name. The kid would have got beaten up all the time for sure with a name like Sartre - is a fighter, and will have to spend some time in an 'isolet' to 'gain and grow'. Both mother and Y-chromosomed oppressor, however, are expected to be fine . . .

Though I don't think the same can be said for the grandmother. Grandmere is slumped beside me in an exhausted heap. In fact, she appears to be half asleep, and is snoring slightly. Thank God there is no one around to hear it. Well, no one except for Mr G, Lars, Hans, my dad, our next-door neighbour, Ronnie, our downstairs neighbour, Verl, Michael, Lilly and me, I mean. '

Mia is very over-protective of Rocky, imagining scenes of injury to him that are unlikely to happen. On her list of people she loves in the seventh book, Rocky is second, below her cat Fat Louie and above her boyfriend Michael.