Summoner is a rather uncommon promoted class in the Shining series. Summoners are obtained by promoting members of the Shaman class.
Summoners are Shamans who have studied and trained enough to summon even certain deities to aid them. The more talented Summoners can also summon larger numbers of spirits at once to cast more powerful spells than they were capable of as unpromoted Shamans.
Few if any generalizations can be made about the people with the title of Summoner, since they are so rarely seen or mentioned, and even the two known examples of the class are radically different from each other in terms of their backgrounds and ways of life.