My family never learned about proper introductions, so every time we added a new cat they would just be let loose to work things out among themselves. Luckily, all of my cats have been very accepting of new cats and here is how it went:
1. We got Elfie in 1997, and he was about a year old at that time. That would make him about 4 when he got our second cat, Rusty, in 2000. Rusty was a runty little kitten, and Elfie thought himself too cool and too tough to be nice to him. He would hiss and swat, never hard, and avoid Rusty. But Rusty was persistent, and just wanted to love on Elfie every chance he got. He would sneak up on him at the food dish and lick his back, causing Elfie to hiss and run away. He would sneak up on him when he was sun bathing or sleeping on the couch, and discreetly cuddle up with him. Man, you should have seen the look on Elfie's face when he'd wake up!! He'd open his eyes to find himself spooning with the runty lil kitten and go bolting out of there all offended
But it only took about a week or two and they were very good friends. Elfie took Rusty under his wing and those two, to this day, have a close, loving relationship.
2. We got Fella in 2004. Rusty must have remembered his experience with Elfie, and what Elfie did for him (was almost like a father to him) because he instantly took an interest in Fella (who at the time was called Cody). He pretended to hate him, swatting him and hissing when he'd come too close. Yet he would seek him out to play with and antagonize- he'd jump onto chairs that were too high for kitten Cody to jump onto and hang his tail over the edge. The chairs were pushed under a table that had a long table cloth that Cody liked to pounce on. When Cody got close, Rusty would friskily bop him. He acted like he hated him, yet he'd follow him around and watch jealously when he played. Just like before, it was about a week or two, and Rusty and Cody were inseparable. As for Elfie- well, he pretty much ignored Cody from the start. To this day, those two are on completely peaceful, neutral terms. They aren't best pals, but they aren't enemies either. They will sit next to each other, but not acknowledge each other. Elfie will wrestle with Rusty, but not Cody. Rusty will wrestle either of them.
3. I got Magneto in July 2008, and he was greeted with hisses and general distrust from everyone. He was pretty scared of them too, so he got to stay in his own room for the first week. Elfie eventually put him in the same place as Cody- neutral. No hisses, but no affection either. Magneto likes to be in Elfie's company, but he respects his "personal space bubble" and doesn't bug him. Fella does not like Nito's antics, and hisses and runs away whenever Nito tries to play. Nito LOVES to chase Fella when he does this. Yet, despite acting like he hates it so much, Fella always jumps up onto the chair and bops Nito to get him to start it up. Then when Nito turns his attention to Fella, Fella hisses and gets all mad and runs away. Silly kitty. All three boys (not Nito) are allowed to wander feely, and without supervision, in our safe back yard. Nito goes out onto the back porch under my supervision, but recently he has gone on short walks with (an annoyed and unwilling) Fella, following him around and staying close. Fella gets fed up and cuts his outside trips short- I guess he doesn't want to be seen by his outside buddies with a little twerp tagging along. Rusty's first encounter with Nito went like this: Nito was on the carpet with some cat nip. Rusty came for some cat nip, walked over to Nito, smacked him across the face and walked off. Nowadays, they wrestle like old pals. Nito, however, is food aggressive, and none of the kitties go near him while he eats, or else he growls like crazy.
Nito lives in a separate city with me most of the time, but whenever we visit home all the kitties remember each other. I've been gone as long as 3 months and they still remember each other. There have not been any really bad hisses or tension since I first brought Nito home. Usually the first one upstairs to greet us when we first get home is Fella. Nito and Fella will lick each other's faces for a few minutes before Fella has had enough, hisses, and runs away. Nito swiftly follows!