Recurring Characters in Seinfeld

Newman

Jerry and Kramer's neighbor Newman (played by Wayne Knight), a portly, vengeful, spasmodic, yet merry U.S. postal carrier, is both Jerry's archenemy and one of Kramer's closest friends. In his first (off-screen) appearance in "The Revenge", Newman was voiced by Larry David, though Knight over-dubbed David's lines for the show's syndicated airings. Newman and Jerry often follow a specific routine of greeting each other, with Newman saying "Hello, Jerry" and Jerry replying "Hello, Newman", both in a venomous tone of mutual disgust.

Newman never misses a chance to get Jerry into trouble. In "The Package," he has Jerry taken into custody by the Postal Inspection Service for suspicion of mail fraud. Nevertheless, he never seems to mind hanging around in Jerry's apartment from time to time as if they were friends. Occasionally, a story places him in the role of a fifth member of the group, though usually he is an antagonist.

Like many Seinfeld characters, Newman is a paradigm of contradiction. On the one hand, he is lazy (he reveals that he doesn't deliver mail when it rains in "The Calzone"), and completely selfish. However, he displays a surprising sensitivity (as in his oft-referenced infatuation with Elaine and the poetry he creates for Kramer in "The Bookstore") as well as wisdom, such as when he decides in a Solomon-esque way to decide the rightful owner of a bicycle ("The Seven"). Newman is once described by George as "merry"; to the audience's surprise, Jerry agrees with this observation ("The Label Maker"). Newman sometimes exits Jerry's apartment with a 'Ta-ta, Jerry!' and a snickering laugh. In "The Reverse Peephole", Kramer notes that Newman is an excellent tree-climber (when Newman is climbing a tree to retrieve a discarded fur coat) and Newman tells him that he learned to climb trees "in the Pacific Northwest." In another episode, Jerry describes Newman's tennis playing ability in the most superlative of terms: "He's fantastic!" ("The Switch").

Others

Estelle Costanza (played by Estelle Harris) — George's nagging and often obnoxious mother.
Frank Costanza (played by Jerry Stiller) — George's hot-tempered, eccentric father
Susan Ross (played by Heidi Swedberg) — George's ex-fiancée who dies from licking toxic envelopes, mailing her wedding invitations
Helen Seinfeld (played by Liz Sheridan) — Jerry's quintessentially Jewish mother
Morty Seinfeld (played by Philip Bruns and later by Barney Martin) — Jerry's father; a retired raincoat salesman
Jacopo Peterman (played by John O'Hurley) — Elaine's eccentric and loquacious boss at the J. Peterman catalog
George Steinbrenner (played by Lee Bear, voiced by Larry David) — George Costanza's boss while working for the Yankees-- a satire of real-life eccentric Yankees owner George Steinbrenner who passed on playing the character himself due to unfamiliarity with the show. He is usually seated at his desk, only seen from the back, gesticulating wildly with his arms.
Uncle Leo (played by Len Lesser) — Jerry's unavoidable and annoying uncle who is known for holding onto your arm when he talks to you.
David Puddy (played by Patrick Warburton) — Elaine's on-again/off-again boyfriend
Mickey Abbott (played by Danny Woodburn) — Kramer's short-statured friend.
Mr. Wilhelm (played by Richard Herd) — George's superior at the New York Yankees
Mr. Lippman (played by Richard Fancy) — Elaine and (briefly) George's boss at Pendant Publishing; later owner of the Muffin Company 'Top of The Muffin to You!'
Mr. (Justin) Pitt (played by Ian Abercrombie) — an eccentric millionaire who hired Elaine as his personal assistant.
Jackie Chiles (played by Phil Morris) — Kramer's lawyer and parody of Johnnie Cochran
Kenny Bania (played by Steve Hytner) — a stand-up comedy hack, and one of Jerry's nemeses.
"Crazy" Joe Davola (played by Peter Crombie) — a "lunatic" who stalks Elaine, George, Jerry and Kramer. At one point he tries to attack Jerry while yelling "Sic Semper Tyrannis!" Named after a real acquaintance of co-creator Larry David.
Sue Ellen Mischke (played by Brenda Strong) - Elaine's rival, she is often referred to as "The Braless Wonder." She is also the heiress to the Oh Henry! candybar fortune.
Sally Weaver (played by Kathy Griffin) - Susan's old roommate from college, In "The Doll" she gives Jerry a giant package that she wants him to take on his plane, even though she was coming up to New York later. She ends up ruining Jerry's bit by bringing the wrong doll to his show and bringing the wrong sauce to New York with her. In "The Cartoon," Sally opens her one-woman stand-up show about "Jerry Seinfeld - the Devil."
Mr. Kruger (played by Daniel von Bargen) - George's boss at Kruger Industrial Smoothing.
Dr. Tim Whatley (played by Bryan Cranston) - Jerry's dentist, whom he suspects converted to Judaism just so he could make Jewish jokes. He's also a "regifter" and a "degifter" in another episode after Jerry gives him Super Bowl tickets.
Lloyd Braun (played by Peter Keleghan and Matt McCoy) - George's boyhood rival, who later ended up in a psychiatric facility. He went out with Elaine, tried to help save a historic theatre with Kramer, and sold computers for Frank Costanza.
Bob Cobb/"The Maestro" (played by Mark Metcalf) — Passionate conductor of the Policemen's Benevolent Association Orchestra.
Ping (played by Ping Wu) — Chinese delivery guy that Elaine crashed into and who serves as a translator for George in his conversation with the Hair Restoration Clinic located in Beijing.
Babu Bhat (played by Brian George) - Jerry convinced him to make an all-Pakistani restaurant and forgot to give him his his immigration papers so he was deported.