Since Desperate Housewives relied so heavily on the narration from Mary Alice Young, the woman whose death kicks off the story and brings the four main housewives together, it makes sense that the dialogue from the first and last appearance of each character has a distinct "beginning" and "ending" feel to it.
These opening quotes manage to introduce characters in ways that are often humorous and matter-of-fact. Meanwhile, their last quotes are mostly bittersweet, which is right in line with the ending of the series as a whole, making both sides fitting bookends.
Mary Alice Young
"My name is Mary Alice Young." - "Most people just go on day after day, trying in vain to keep secrets that will never stay hidden."
Mary Alice Young is the narrator of the series, even though she's dead for all of it, save a few flashbacks. The show kicks off on the day of her funeral after she's taken her own life because she received a threatening blackmail note. Without this mystery, there would be no show, so it really does all start with Mary Alice.
As Mary Alice narrates the protagonists leaving Wisteria Lane in the series finale, the woman who moves into Susan's old house looks over her shoulder before hiding a box in a cabinet. This suggests that there will always be secrets and drama in Wisteria Lane.
Lynette Scav0
"Stop it, stop it, stop it, stop it, stop it!" - "I am so crazy nuts about you guys. Promise me this is not gonna be the last time we play poker together."
Lynette's first line comes in the midst of her introduction, narrated by Mary Alice, who describes her friend as a former businesswoman who is now a housewife with unruly young children. This first line illustrates Lynette's bossy, assertive personality, as well as her frustration with her poorly-behaved kids.
This sweet sentiment from Lynette comes during the group's last poker game before Susan, and gradually the rest of them, take their final leave of the Lane. Her friends echo the sentiment, but ultimately the promise isn't followed through.
Carlos Solis
"If you talk to Al Mason at this thing, I want you to casually mention how much I paid for your necklace." - "That’s easy. You and me? We’re doing a tango."
Carlos is introduced as a vain, selfish man who only cares about his work and his wealth. He gives his wife Gabby this instruction while they're on their way to the funeral of one of her best friends.
This is Carlos' response to Gabby's question of why things seem so hard for them in their marriage compared to everyone else. Although to be fair, two affairs, prison time, birth-control tampering, a miscarriage, divorce, blindness, and finding out their daughter was switched at birth still doesn't actually make Carlos and Gabby's relationship the most tumultuous on the lane.
Gabrielle Solis
"Why don't I just pin the receipt to my chest?" - "We'll just have to make the time."
Gabby answers Carlos' first line with this witty rejoinder. This establishes her sassy nature, resentment of her husband, and her sharp sense of humor. Gabby is unsatisfied with her marriage at the start of the series because she feels that her husband views her as another acquisition and not an object of love and affection.
This is Gabby's assurance to her friends that they will meet again. This line foreshadows how busy they all become in the near future: Susan is helping Julie raise her baby, Lynette takes a job in New York, Gabby becomes a famous fashion influencer, and Bree gets involved in politics.
Bree Van De Kamp
"It was no trouble at all. Now, the basket with the red ribbon is full of desserts for your guests, but the one with the blue ribbon is just for you and Zachary. It's full of rolls, muffins, breakfast-type things." - "Of course we will."
Bree is introduced as the perfect homemaker with an unhappy home life. Her family resents her perfectionism, but she doesn't seem to notice or care. She is the person who always brings baked goods, even bringing two different baskets to Mary Alice's funeral.
This was Bree's assurance to her friends that they would all meet again to play poker and gossip together. As Mary Alice informs viewers via her narration, it was not to be. Perhaps it was Bree's politeness that drove her to make this promise, or perhaps she really did plan on making the time for another gathering in the future. Either way, this last line is a bit ironic because the four friends never played poker together again.
Susan Mayer
"Well, sometimes people are so unhappy they think that's the only way they can solve their problems." - "Hey, do you guys mind if I take one last spin around the block?"
Susan's first line is an answer to her daughter Julie's big question about why a person might take their own life, while they're on their way to Mary Alice's funeral.
As Susan, Julie, M.J., and Julie's newborn baby are all packed in and buckled up for their move from Wisteria Lane, Susan feels sentimental about leaving her home. She asks her kids if they'd mind waiting while she drives around the block one more time. In a very sweet (or very strange, depending on how you look at it) scene, the dead of Wisteria Lan wave goodbye.
Mike Delfino
"No, I just refuse to believe that anybody can screw up macaroni and cheese... Oh, My God. How did you... it tastes like it's burnt AND undercooked." - "Tomorrow."
Mike Delfino is introduced via a meet-cute with Susan Mayer (who would later become Susan Delfino) at Mary Alice's funeral. Susan brought her infamous macaroni and cheese, which she attempts to dissuade Mike from eating. This is his real-time response to trying her food.
Mike's last words before he's shot on his front steps are in response to Susan asking him to fix their fence post. Prior to this, they have a sweet conversation about how much they admire and love each other, and fans just know something bad is going to happen. Susan is just about to say something to Mike when the loan shark he pissed off shoots him in a drive-by.
Edie Britt
"Hello there!" - "I'm gonna tell him before you... before you do something stupid."
Edie's introduction is definitely played for humor. After Mike and Susan's meet-cute, Susan goes to pay Mike a visit. While she's talking to him on his front porch, Edie comes jogging attractively up the sidewalk, with a cheerful "Hello there!" She quickly makes her intentions on Mike clear to Susan through her not-so-subtle maneuvering.
Edie's return to the Lane with a shady, creepy new husband was bound to end poorly, but few expected it to end with her death. Edie finds out Dave's secret: that his wife and daughter were killed in the accident Mike and Susan were involved in, and that he came to Wisteria Lane for revenge. Edie tries to call Mike to warn him, but Dave starts to choke her and she flees the house.
Andrew Van De Kamp
"Who asked you to spend three hours on dinner?" - "Actually, I’m more interested in Geoffery with a ‘G’."
Andrew spends the first few seasons as a rebellious teenager with a bad attitude. When Bree is complaining that nobody appreciates her above-and-beyond efforts around the house, Andrew replies with this rather rude question.
Andrew and Bree's relationship comes a long way by the end of the show. When Andrew first came out to his mom, she tried to convert him to be straight and told him that he would go to hell if he didn't change. Over time, she was able to accept his sexuality and support it. She eventually hired him to help run her business and purchased a home for him and his fiancé. When Andrew tries to go back into the closet so he can secure financial support from a rich girlfriend, Bree tells him that he doesn't need to hide who he is and that she'll help him get back on his feet. This conversation where they talk about the guys Andrew is attracted to shows how far these two have come.
Tom Scavo
"I have to go back to 'Frisco in the morning. But I got your call, you sounded a little frazzled." - "I bet someone like that would be happy anywhere. Even New York."
Tom's introduction comes during the pilot when he pops in to see Lynette after hearing she's struggling with the kids. He doesn't do much to help and just barges in expecting sex, which is kind of Tom's M.O.
Tom finally lets Lynette do what she wants to do in the finale. She's willing to give up her career yet again for him, but he decides to support her in her new opportunity, and they move to New York.