I've been thinking about how in several different tales, a Thumbling figure becomes a favored servant of a king.
Tom Thumb becomes King Arthur's dwarf and one of his favored knights. (In later versions, he runs afoul of the queen.)
Issun-boshi acts as a samurai for a daimyo, or feudal lord.
The Hazel-nut Child, in a tale from the Armenian people of Romania, Transylvania and the Ukraine, makes his way to the palace of an African king. Like Tom Thumb carrying home a coin for his parents, the Hazel-nut Child brings home a diamond given to him by the king.
Karoline Stahl (the same woman who wrote the first version of Snow White and Rose Red) wrote a story called Däumling. Daumling goes to live in the palace, where he serves the king and several times defends him from assassination attempts. The story was probably inspired by the British Tom Thumb.
Both stories have an emphasis on the main character's clothing and needle- or pin-sized sword, as well as an evil queen.
Sometimes the thumbling's encounter with the king isn't quite so pleasant. In numerous tales, the thumbling is out in the field with his father, when a rich man, sometimes a noble or king, sees him and asks to buy him. The thumbling sells himself and then runs away, cheating the rich man.
In one version, Neghinitsa, the main character does not run away, but ends up working as a king's royal spy until his death.
In other stories, like the German "Thumbling as Journeyman," or the Augur folktale "The Ear-like Boy," the Thumbling becomes a robber and a king is one of his victims. In a tale from Nepal (printed in German), the thumbling steals items from the king's palace and eventually wins the hand of one of the princesses.
Also in "Thumbling as Journeyman," the little thief takes a single kreuzer, stolen from the king's treasury, to give to his parents back home. Here again is the same motif as Tom Thumb, where the tiny knight asks King Arthur for permission to take one small coin to his parents.
In other stories, Thumbling marries the king's daughter - a common ending for fairytales.
Issun-boshi marries the daimyo's daughter.
In the Philippines, Little Shell and similar characters pursue the daughter of a chief. (See blog post.)
In India, Der Angule completes many tasks for a king and finally marries the princess.
Some retellings of Tom Thumb, such as Henry Fielding's play, have him woo a princess.
I worked a little bit on a chart comparing some of these stories. I included the Grimms' Thumbling among "trickster tales." EDIT: Now with new and improved chart!
Researching folktales and fairies, with a focus on common tale types.