The Rankin family were English nobility. In the early 19th century, the head of the family held title as the Earl of Kensington, a title that dated from the 12th century.
The earl's third son, Jeremy Rankin, stated that the family had "always sent third sons to the Corps" and once kept their own dragons, four or more generations ago, before the private ownership of dragons was abolished in Great Britain and all dragons were inducted into the Aerial Corps as "property of the Crown".
Celeritas and his captains
Jeremy Rankin's grandfather was the first captain for the dragon Celeritas. A son of this first captain also served with Celeritas, presumably as his second captain. Aviators in active service were generally unable to administer estates or hold other official duties, so it is highly unlikely that either of these men ever held the title of Earl; Celeritas' second captain was probably Jeremy Rankin's uncle.
If both of these men belonged to the Rankin family, then either the direct line of primogeniture was disrupted in the past three generations (i.e., the first captain's older brothers died without male heirs and one of his other sons inherited the title) or the first captain was Jeremy's maternal grandfather rather than paternal (i.e., the first captain had a daughter who married her most senior male cousin and became Countess of Kensington).
The Rankins had considerable political influence. Jeremy Rankin's mother insisted on keeping at home longer than most young aviator candidates, which was later blamed for giving him "strange notions". In the normal course of events, Jeremy Rankin would have inherited his uncle's captaincy but Celeritas rejected him, ultimately retiring from active service to become a captainless trainer at the Loch Laggan covert.
Celeritas later told William Laurence that Jeremy "ought never have been an aviator, much less a captain". However, Celeritas did not voice his full objections at the time and Aerial Command reassigned the boy as a courier at age 12, giving him a Winchester whom he named Levitas.
After Levitas' death in 1805, which was partially attributable to culpable neglect, the Rankin family again used its influence on Jeremy's behalf to get him a new dragon. Jeremy was sent to New South Wales, arriving in late 1809 oe early 1810, and given priority for the eggs that had been sent with Laurence on the HMS Allegiance. The first hatchling accepted him, though it rejected his proposed name of "Serenitus" and insisted on naming itself Caesar instead.
Nothing is currently known of Jeremy Rankin's two older brothers, or any nephews who might supply the next generation of aviators from the family.
Deviations from history
There is no definite historical record of a hereditary Earldom of Kensington in Great Britain. The titles "Baron Kensington" and "Earl of Holland" were created ~1624 for Henry Rich, a younger son of the Earl of Warwick. A single source states that he was created "Earl of Kensington" at that time, but without other corroboration; "Baron Kensington" is the title cited for his subsequent heirs.