The scene where Tom and Partridge happen upon a Roma wedding in Book 12, Chapter 12 gives Fielding a chance to think about power and authority from an outsider perspective. The rest of the novel sketches out various levels of English society, which the reader is supposed to recognize and know. But this gypsy wedding is a moment of exotic foreignness. (We talk a little bit about the giant problems of Fielding's stereotypical portrayal of the gypsies in our "Detailed Summary" of Book 12, Chapter 12.)
As Tom looks at the king of the gypsies, he notices that there is an authority about him, even though he isn't wearing "any regalia of majesty to support his dignity" (12.12.19). (In other words, he isn't wearing a crown or uniform of any kind.)
The narrator wonders briefly: does the king's air of power come from the fact that his subjects respect him, or do his subjects respect him because he has an air of power? It is because Tom and Partridge have been placed in a totally unfamiliar setting that the narrator has a chance to question our basic assumptions about the links between appearance, authority, and power.
The language of the king of the gypsies immediately sets him apart from the other characters in Tom Jones. He sounds uneducated and rough. (Seriously, Fielding's use of accents here is offensive: "Me vil" instead of "I will" (12.12.34)? Come on, Fielding.)
Fielding uses the king's accent to draw a contrast between the apparent ignorance of his speech and the wisdom and straightforwardness of his ruling decisions. The narrator admires the gypsies' social emphasis on honesty and plain dealing among their people. At least they don't "rob one anoder" (12.12.34), as the English folk in the rest of the novel are so happy to do.
Fielding's portrayal of the gypsies is definitely biased and condescending. Yet, he mostly includes them so he can satirize the lying and the dishonesty of the English—the main target of Tom Jones's mockery.