DM's, Do your PCs realize there are Bigger Fish?

[Primitive Screwhead]

Corsair Only if the bigger fish are worried about the small fry PCs.. in which case the PC's should be paranoid.

If, on the other hand, the bigger fish are busy messing with the other bigger fish... then the small fry PC's get left well enough alone. They might even end up being the biggest fish in that nice little backwater town with the high quality inn....

If you want to be the biggest fish in the pond, stay away from the ocean and find a nice little puddle to splash around in.

 

[Quartz]

It sounds like the OP's player might be better off playing Amber...

 

[Lord Pendragon]

how oftten do you have you pcs encounter more powerful or vastly more powerful npcs.

Very, very rarely. I think the point of gaming is to let the players be the heroes of the story. I want them to always feel like the big fish. At low levels, it begins as "big fish in a small pond" where they know little of the world--perhaps just their own village/town--but are the elite of that world. As the campaign progresses, their "big fish" status remains, but the sphere to which it applies grows larger and larger, until by the end of the campaign, there are no bigger fish.

That said, naturally I occasionally find the need to introduce a more powerful NPC. But only sparingly when no other means of accomplishing that task presents itself, and later I give the PCs the chance to see that the tables have turned.

what are your main reasons for introducing a mighty npc?

To introduce plot threads or present adventure hooks. Never to bail out the PCs or overshadow them.

Do you keep your pc egos in Check?

Edit: Well, in the sense that you mean, toning down the backgrounds for 1st-level characters, then yes. I remind them to keep the pond small at first, and promise them that it will get bigger over time.