Malachi Constant
The novel's central figure. He starts as a passive beneficiary of luck and ends as a man who has lost everything and found a small, quiet peace. He never really drives the plot. The plot happens to him, which is exactly Vonnegut's point.
Winston Niles Rumfoord
The architect of the novel's events. After flying into a chrono-synclastic infundibulum, he can see all of time and uses that knowledge to engineer a new religion and reshape human society. He's brilliant, manipulative, and ultimately also a pawn in a larger system he didn't design.
Beatrice Rumfoord
Winston's wife, who starts as a proud, aristocratic woman and ends up stripped of wealth and status, living on Titan. She responds by writing a book that finds meaning in her own experience on its own terms. Her arc is about dignity without illusion.
Boaz
A soldier in the Martian army who ends up trapped on Mercury with Malachi. He finds genuine purpose caring for the harmoniums and chooses to stay when escape is possible. His choice is one of the few truly free acts in the novel.
Salo
A Tralfamadorian robot stranded on Titan for hundreds of thousands of years. He's been waiting for a spare part the whole time. He develops real affection for Rumfoord and later for Malachi, and his self-destruction after learning the full truth about his mission is the novel's most emotionally direct moment.
Chrono
Malachi and Beatrice's son, born on Mars. He carries a piece of metal as a good-luck charm without knowing it's the part Salo needs. He's largely a plot device, but his indifference to human civilization and his attachment to the charm make him a small symbol of the novel's themes.