In The Lottery, the lottery itself, is a character, it appears to have established itself, firmly in the town, this ritual continues even though the townspeople can't remember why the tradition is held, nor for what purpose they are preserving it. But, the lottery persists, either out of fear or out of a sense of obligation, a town tradition that has found a way to equate itself with picnics, square dances and parties.
"The lottery was conducted--as were the square dances, the teen club, the Halloween program--by Mr. Summers. who had time and energy to devote to civic activities. He was a round-faced, jovial man and he ran the coal business, and people were sorry for him. because he had no children and his wife was a scold." (Jackson)
As the main character in the story, the plot revolves around the lottery. The lottery supersedes all other characters, it is more important than any one in the story. It must be held, it must be honored, it must be satisfied.
The reader, by the end of this story, learns more about the lottery, the ritual execution in this town, than any other character.
This insidious evil has become as regular as a church picnic, the people in the town have become immune to the destructive nature of the lottery, sacrificing their humanity to engage in a yearly ritual murder.
Shirley Jackson's "The Lottery" is less than 4000 words so there is little time for heavy character development. Even the ones mentioned in the question- Old Man Warner, Tessie, and Mr. Summers- are dependent on stereotypes. The remaining townsfolk, a few of which we do hear from are even more stereotypical.
Mr. Adams, the first man to draw, says to Old Man Warner that they are giving up the lottery some places. We get the feeling that his wife and he are a bit in favor of this idea, but they meet Old Man Warner's scorn. They give lip service to what is right, but they still follow through with the lottery.
Mr. Graves helps Mr. Summers. His name shows a stark contrast to Mr. Summers just as the lottery itself shows a stark contrast in the summer day and the grisly events to follow. Mr. Graves, like everyone else, participates in the lottery.
Mrs. Dunbar draws for her husband who has a broken leg. When they are NOT selected, she sends her sixteen year old son to tell her husband, Clyde, that it will not be them. One can only imagine what Clyde might expect if he had been drawn. Indeed, the town would have likely descended on his door step.