Breakfast Princess is the princess of Breakfast Kingdom. She rules with her sister Toast Princess and they, like most princesses, are often bothered by Ice King and need Finn and Jake to get rid of him. This is implied in the beginning of "Hitman," when Breakfast Princess says "I've got another Ice King situation here."
Breakfast Princess has egg-white hair and egg-yolk skin. She has bacon on her head which would appear to be used as a crown and a top consisting of buttered toast and a bacon belt. Her skirt looks like a pancake with syrup on it while her shoes resemble cracked eggshells.
Originally, there were two designs that Pendleton Ward posted on Twitter (see picture below). The toast version was designed by Ward himself and the current version by Cole Sanchez. Evidently they decided to use them both, with Pendleton Ward's design becoming Toast Princess.
Breakfast Princess appears in Issue 3 of the comics.
The original version of Breakfast Princess has straight hair with a short, front fringe and two long bacon earrings, however no bacon crown. Also, her skirt has a big chunk of melting butter.
Unlike most princesses, Breakfast Princess does not have a gem of power in her crown, that may most likely be due to the fact that it is made purely out of bacon.