The final quest to get yourself a King or a Queen (depending on which gender you are), involves capturing a level 10 NPC. There are a range of quests before this which must be completed before unlocking this quest. The quest beforehand is to capture a level 8 NPC is that is relatively easy to do. However capturing a level 10 NPC is much harder at the start of the game as you will probably have very low gear and stars meaning very big losses without a life bonus. There are a number of things you can do to make it much easier for yourself to do. For starter make sure your city is right next to the level 10 NPC, in other words 1 mile away. This can easily be achieved by just waiting for a flat beside you to reach level 10, then capturing it and building a city on it, then abandoning it. The level 10 NPC will now remain until server maintenance giving you plenty of time to capture it if you do it early in the day. A standard archer rainbow should take it down easily but your losses will depend on your stars. Try to have a hero with at least 200 attack, fairly easy considering a hero at level 100 and a base attack of 69 with all gear upgraded to level 2 should reach around this total. You really should try to use a level 90+ hero when attacking to make sure you troops have full leadership. Loyalty waves can be done very easily with warriors or a small number of archers.
King / Queen Benefits
Stronger than any normal hero as they have 85 base in all their stats (Not nearly as strong as Historic Heroes though)
No loyalty on this hero so they cannot be lost through attacking another player.