The Martian Chronicles
Ylla, Captain Jonathan Williams, Captain John Black, Jeff Spender, Captain Wilder, Benjamin Driscoll, Tomás Gomez, Muhe Ca, Father Peregrine, Stendahl . . .
We could go on. Every story has a protagonist, and each one has a different one.
Most of Bradbury's positive protagonists have certain things in common: they're thinkers, they're nonconformists, and they're curious people who don't let themselves be constrained or deadened by custom. He puts us in their heads and usually we're happy to be there.
Take Mr. LaFarge, for instance, who wonders about the Tom-shaped-Martian: "Who is this, he thought, in need of love as much as we? Who is he and what is he that, out of loneliness, he comes into the alien camp and assumes the voice and face of memory and stands among us, accepted and happy at last?" ("The Martian," 109). Mr. LaFarge is a nice-sounding man. We like spending time with him and we're a little sad when "Tom" dies.
But not all the protagonists are sympathetic. Stendahl, for instance, is bent on revenge: "Oh, how the anger and hatred had grown in him through the years. Oh, how the plan had taken a slow shape in his numbed mind" ("Usher II," 95). But we still have to sympathize with him a little, since (presumably) we agree with him that censorship—particularly book-burning—is wrong.
The best way to figure out if someone is a protagonist? See if Bradbury is letting us inside his or her head.