1. William (The Netherlands): He has never backstabbed me once and is very easy to get along with. Even if you choose an ideology that he disagrees with, you can still remain friends with him. Just don't be an outrageous warmonger and you shouldn't anger him

2. Pacal (The Maya): Another one of your most trustworthy choices for an ally. He is easy to befriend and stays loyal througout the whole game. However, I think part of the reason why he is loyal is becuase he never amasses much of an army to use.

3. Harun al-Rashid (Arabia): On this list basically for the same reasons as William and Pacal, but more likely to focus on trade with your empire, due to his bonus.

4. Gustavus Adolphus (Sweden): Not only is his base loyalty high to begin with, he is also very tolerant of warmongers. This was because he was meant to be a warmonger, but due to his low expansion,he tends more often to be peaceful.

5. Ahmad al-Mansur (Morocco): Another civ who focuses on trade more than average. Your friendship with him may arise from a trade route or two, or just because of his high likeliness to be friendly and loyal.

6. Harald Bluetooth (Denmark): Although he can be aggressive, he is very loyal to his allies. This is rare for a warmonger, but it is the case with the next three civs as well.

7. Alexander (Greece): Harald Bluetooth 2.0, except he is more likely to succeed in wars and keep a strong army. He can be a loyal ally in wars, and send his army around the globe to help you fight that civ who just backstabbed you.

8. Askia (Songhai) Almost always loyal, but he does have a tendency to become guarded for small reasons. He is also not very tolerant of differing ideologies.

9. Genghis Khan (Mongolia): I know some people claim he backstabs like it's 50% off diplomatic penalties at Warmongers 'R' Us, I have never seen him do it once. I'm not sure why I have such different experiences with him, but I write what I observe in this guide. He almost always defends his allies against their foes (but not their city states) and rarely denounces fellow warmongers.

10. Sejong (Korea): Like Askia, he is always loyal in the early game, but his loyalties may falter if he sees you as a threat (and he feels threatened pretty easily).

11. Boudicca (The Celts): Although not very easy to befriend, she is loyal to her allies (of which there are few). If you do manage to become friends with her, realize she is not very forgiving either.

12. Ashurbanipal (Assyria): He has proven many times that he would rather march his army to the other side of the world before attacking a weaker ally. The reason why he isn't higher on this list is because I haven't seen much of him. He usually dies before he makes any friendships.

13. Gandhi (India) Yeah, he's here. Although not very tolerant of warmongers, he isn't nearly disloyal as people claim.

14. Maria I (Portugal): I was uncertain where to put her on the list because of her erratic AI. My experiences with her differ from game to game. Most of the time, she is loyal. In some cases though, she can backstab at seemingly random times.

15. Pedro II (Brazil): He can be loyal about 70% of the time. Unfortunately, he tends to plot against EVERYONE, and that often leads to backstabbing his allies. This usually takes the form of denouncing and not outright declaring war.

16. Maria Theresa (Austria): This is a tough one. She is loyal for the most part, but she is willing to denounce anyone, even her allies, for small reasons. She also has a habit of waiting until a declaration of friendship (I will abbreviate it as DOF from now on) expires before declaring war on past allies.

17. Haile Selassie (Ethiopia): Here for the same reason as Pedro II. He plots against most other civs, and denounces his allies for little reasons. He can sometimes be loyal, but can denounce then declare war on his allies if he thinks they are a threat.

18. Darius I (Persia): I am probably going to regret putting him this high on the list. He is loyal in the early game for sure, but he doesn't intend to keep friendships for very long. You will find in the late game that he befriends people to use them, and will denounce and then declare war on those who he feels threaten his victory, even if he was friends with them.

19. Isabella (Spain): She is somewhat erratic when it comes to loyalty. I have had games where she has been my ally for most if not all of the game. In other games, she has backstabbed me usually through denouncing.

20. Ramkhamhaeng (Siam): The only reason he is loyal is because he usually has a puny army, or has lost his capital. He is notoriously difficult to get along with, and even if you do manage to stay friends with him, he is one of the neediest civs I have ever met.

21. Wu Zetien (China) Having one of the lowest loyalty ratings in the game, she is surprisingly not as backstab-prone as you might think. She can denouce her allies for petty reasons in the late game, but more often then not, she just ignores those who don't bother her.

22. Theodora (Byzantium): One of the most friendly leaders in the game, and also one of the leaders most likely to denounce allies for the smallest reasons. I hate how she denounces you while friends, and then immediately wants to be your friend again. I don't know how that makes sense in her head.

23. Elizabeth (England): Another culprit for denunciation overkill is Elizabeth. Unlike most civs, she will denounce you simply because she had a bad day. There are rarely reasons behind her denunciations. If you manage to befriend her, don't expect her to keep her word.

24. Nebuchadnezzar II (Babylon): Well, he has never backstabbed me. The only reason for that is because I can never befriend him in the first place. However, I see him backstab other AIs all the time. He usually declares war on weak allies rather than denouncing them first.

25. Pachacuti (The Inca): He can be loyal sometimes, and I stress sometimes because it is mostly due to weakness. He is just afraid of being conquered. He loves to wait until a DOF expires before attacking a former ally, and sometimes denounces them if he wants the world to gang up on them.

26. Attila (The Huns): Let me explain before you write that comment. I have heard terrible things about his disloyalty, but I have rarely experienced it myself. I put him here because of everyone elses experiences with him. This is the only case of that.

27. Cathrine (Russia): One of the more notorious backstabbers in the game is Cathrine. She is meant to be very deceptive, but often waits too long for that to show. as a result, she is SLIGHTLY more loyal than she was meant to be. She often denounces allies before declaring war on them, but doesn't usually declare war on them outright.

28. Enrico Dandolo (Venice): Meant to be backstabber #1 of the BNW expansion, Venice really loves to deceive their allies. He is plotting against you from the day you meet him, and is just waiting for the right time to strike. He always denounces allies before revealing his true colors to you. A declaration of war from his is rare, though.

29. Casimir III (Poland): Barely squeaking his way on this list is Casimir. I honestly don't know how his loyalty rating is a 7. He has never had any semblance of loyalty in my games. Backstabbing weaker allies, denouncing stronger allies who he feels threaten him, and just being a pain in general have earned him this spot. I just put him here becuase he might be glitched or something.

You may ask why some civs were on the last section of the list instead of this one. I reserved this portion for those who have declared war on me WHILE we have a DOF going. There is only one exception to this, but you will soon see why.

30. Ramesses II (Egypt): Having only done this once, Ramesses occupies the least worst spot on this list. He is usually disloyal to begin with, and loves to denounce his friends for insignificant reasons.

31. Pocatello (The Shoshone): I believe he was never meant to be a backstabber or as warmongering as he is. Due to his high expansion rating, he loves land, YOUR land. If you are his neighbor, always be watchful for him. He likes to wait until your DOF is over, but he might just declare war on you while it is still going on instead.

32. Washington (America) MY wanton aggression??? If you want to keep your friendship with Washington, keep a strong army. If he detects the slightest bit of weakness in his allies, he will attack them. Having one of the largest armies in the game, this isn't hard for him to do.

33. Napoleon (France): Every mode of backstabbing is open to this guy, although he prefers not to declare war while a DOF is going on. He isn't higher on this list becuase he usually attacks those whom he dislikes first.

34. Hiawatha (The Iroquois): He is very consistent in declaring war on me while we have a DOF. Since his expasion rating is the highest in the game, he backstabs all the time if he wants land. Watch out for him in the early eras of the game. He will build mohawk warriors like they're free, and he isn't afraid to use them against a weaker ally.

35. Gajah Mada (Indonesia): Time and time again have we been friends and neighbors, and he backstabs me almost immediately. We are lucky as players that he sucks so badly at fighting. It doesn't take much to send his armies packing. Once you do, he usually wisens up, but he still hates you. I recommend just wiping him out instead of making peace.

36. Montezuma (The Aztecs): Everyone hates him, and I know you do too. He is extremely aggressive and disloyal, liking to declare war on his friends rather than denouncing them first. The reason why he isn't lower on the list is due to his tolerance of warmongers. Most of the other civs here will denounce their fellow warmongers in order to justify attacking them. Montezuma doesn't do this because he doesn't need to justify attacking you. He simply doesn't care.

37. Dido (Carthage): Firaxis made her so disloyal and aggressive because historians aren't even sure she really existed. There isn't anyone who will be angry about a character from a myth being so evil. When Dido wants to throw her elephants around (the real things, not her...), she doesn't even consider friendships. Any neighbor to her should be wary of her deceptive tendencies.

38. Kamehameha (Polynesia): Here he is, our one exception to the declaring-war-on-me-while-we-are-friends rule (but I did see him do it to Brazil once). I put him here because I hate him. I once thought he only backstabbed allies who he thought were warmongers. However, I quickly learned that he will backstab anyone for any reason. If you take over any city while you and he are friends, he will denounce you. If he covets your lands, he will denounce and attack you. If he decides to choose autocracy, which he usually does, be ready for him, even if you two are friends.

39. Sulieman (The Ottomans): I recommend just not befriending him at all. He is always hungry for more land, and the lands of his friends taste all the sweeter to him (No, It's not a fat joke). A backstabber in both the early and late eras of the game, he loves to declare war outright on friends. As soon as he researches gunpowder, be ready for him to storm your lands with janissaries.

40. Bismarck (Germany): He is like another Suleiman when his loyalties are put to the test. He edges him out slightly because he just doesn't give up. If he attacks you, he will not stop pounding you with units until you surrender. If he does wind up backstabbing you, he will make no attempt to reconcile it either.

41. Oda Nobunaga (Japan): Aggressive like you wouldn't believe, and he has no remorse when backstabbing his allies. You would think a 16th century samurai would value honor a bit more. He seldom bothers denouncing his allies, and instead prefers to attack them when they least expect it.

42. Shaka (The Zulus): Fun fact: Shaka has the highest loyalty rating in the game at 8. It is a wonder how he turned out like this. He is by far the most aggressive leader in the game, even more so than Attila. This coupled with his extremely high expansion rating lead him to backstab his allies way more than he should. He denounces for the most trivial reasons if you aren't friends with him. If you somehow manage to befriend him, he will backstab you. Not might, WILL. Even if you share an ideology, you are still not safe from him.

43. Augustus Caesar (Rome): What I hate about our #1 backstabber the most is his apathy. If he has two neighbors, he will attack one and befriend the other. Once the first war is over, he is guaranteed to backstab his ally. There isn't a chance that he will try to keep that friendship going. At least Shaka tries to gain something from your friendship. I hate him because he is so predictable. With other backstabbers, you may be surprised when they reveal their deception. With Caesar, you will always see it coming. He makes for a very boring and predictable backstabber, which i feel is even worse than an erratic one (erratic backstabbers are fun).

Find this guide helpful? Try something completely different! I have a Youtube channel:
http://www.youtube.com/TheGreatWallOfChins
Steam group: http://cs2bus.com/groups/tgwoc

I also have an upcoming guide about military strategy in Civ V that is approximately one whole game too late.