I know of the Dragon Knight. Found a dragon and joined them. One helluva life. Probably the most dangerous, but adventurous kind.

Now, what is the knight called if they betray the dragon(the killed it kind- after making a fearsome reputation with the dragon)? 

[INSERT NAME HERE]

Second: That very said person then joins a mercenary company. 

[INSERT NAME HERE]

I would think the Paladin version to what I am asking of you guys is: The dragon died in battle and so the Dragon Knight carries on on foot. Regardless of what affiliation the dragon was (chromatic, excetra) the Knight strove for peace after their dragons death as to the fundamentality of the 'why' the dragon allowed a Dragon Knight to take place. Or however you say it.