>>96333419 (OP)
What game? What setting?
A Pendragon or L5R game is about noble warriors doing adventures, whereas a noble PC in Delta Green would be pretty hard to justify unless they're some sort of limey wanker.
In a general pseudo-medieval fantasy game a noble PC is pretty easy to justify, though. Exiled nobles seeking the coin and connections to reclaim their seat, younger sons with nothing to inherit seeking their fortune, bachelors on the mannerbund, eccentric nobles seeking a legendary treasure or writing a travelogue, a young noble fleeing an unwanted marriage: the possibilities are legion.
They are also useful. A noble is a patron who can more easily fund equipment for an early party, a face for interacting with high society, and a heavily armored warrior for combat. They're also a natural nexus for diverse supporting characters like experts in the wilderness, people good at ranged combat, and people who can infiltrate places a noble can't.
In fact, one short campaign I ran (in Mythras) featured a GMPC noble to help fill these roles, although if its not a PC they need to have some major flaw that makes the PCs the main characters. In that campaign I had him as an extremely old man seeking a treasure he had narrowly missed out on as a young crusader. He was able to provide decades old half forgotten insights to keep the party on track and use his status to help the party sometimes in social situations, but was otherwise more of a burden than a boon until his untimely demise just in sight of the ancient tomb. If you do this, I'd suggest making them some combination of old, insane, crippled, dying, stupid, arrogant, or the mark so that the players have to manage and work around the aristocratic GMPC
