The Guardians (not to be confused with Guardians of Owa) are the founders of the Omnitrix Guardians (original, Nega, and Galactic.) If they are in the pressence of any of their underlings, like any of the members of any of the 3 guardians, those underlings must bow to them, even if they are loyal to any one else.
They were once friends with Azmuth, but they could not stay long, for their mere existance upset the natural order of things, so Azmuth offered to create the Omnitrixs for the Guardians so they could help those that can't help themselves, thus all Omnitrix Guardians were created.
They are the ONLY Omnitrix Guardians in the universe who actually DON'T wield Omnitrixs. They are already powerful as they are. In fact they're so powerful, that they even surpass the Titans, Krons included. Of course, Kronos knows this, so he won't dare challenge them. But, he does know their weakness. They get their strength from a small orb that if taken away, they slowly lose their power. So they hid it, but unfortunately, Kronos knows where it is. So he sent Johnny to get it, and now they are slowly losing their powers, and if this continues, within two months, they'll be so weak, that Kronos will be able to destroy them without without really trying.
Since they don't like messing with the natural order of the universe, if they meet any of their underlings, all they want is respect. They don't care what side their on, they just want for them to bow to them, and to tell them what has happened since their last visit. After that, they can go back to their original leader. But if a guardian gives an underling an order, it must be followed, or the underling will lose their Ultimatrix, and must lead a normal life in their own way. Don't be fooled, they are VERY good, but very mysterious, so Kronos see's them as his most powerful enemies, and the worst thing since "easy" open ovens. He hates them most of all.