By name.
My cat responds to his name, and also to “cat.” “Snack” is also a big winner.
My cat’s name is Kitty, so yes and yes.
That made me laugh way too much (probably because my husband’s cat likes to experience the world with her mouth, too). 
Both of my cats know their names, but they also know that if I’m calling for one of them in the kitchen, there is food involved, and I’ll get both of them.
I think you are being a speciesist without really realizing it. I’m quite sure that both cats are very intelligent. The one you believe isn’t, is no doubt ignoring you and will continue to do so until you realize the grievous error you made so many years ago. Since I see no reason that both of you should continue to suffer, I’ll just tell you.
You named him Lloyd. 
Finally, someone who gets it.
The inferior species must adapt to the superior species, not the other way around. It never even occurred to me to speak human to my cat. I almost always meow. But since cat is a tonal language, execution has to be precise. The difference between ‘your coat looks lovely today’ and ‘you look like a walking hairball’ is virtually infinitesimal.
dzero, you should meet him! He’s totally a Lloyd. 
Both my cats do not respond to their name. However, both come to non-verbal cues (the big one to rubbing your fingers together the little one to light clapping) so they can be called.
(Though little one is rarely more than five feet away from me so it’s not much of a feat for her.)
Meanwhile, all the talking he’s doing is HIM trying to teach you HIS name!
Silly humans.
We call our two cats all kinds of names. Not 100% on whether they recognize and/or respond to them specifically, though.
I sometimes call the Neville kitties by their names, and sometimes call “Babies!” when there is food to be had.
Luna, our fat cat, responds both to her name and to Katya being called. I think she has figured out that, most of the time when we call Katya, it’s to give her some food or a treat that we don’t want Luna getting. Luna, of course, does not approve of this plan.
I do this, too. Our cat responds to his name as well, but he takes his sweet time about it.
Both our cats (Al and Nikki) know and respond to their own names and to their chief respective nicknames (Alfie/Alpo and Pookie). I don’t call any cats, mine or strangers, with “here, kitty kitty.” Instead, I use a little kissy sound that seems to be well-received.
I have to add that the Sibilants and Trills is when I’m calling to them. When one of them does what they’[re not supposed to, they get yelled at my name. Which is, I suppose, another good reason not to get them to come by calling their names.
I knew a cat, who lived next door to me when I was a grad student, who definitely responded to his name. When he saw you coming, he’d run away, until you called his name. I suppose this proved that you knew him. But, after all, if this cat didn’;t know me by sight and smell, why would calling his name be the deal-clincher? Whatever the reason, if you didn’t say his name, you couldn’t approach him.
Here Puss, Puss Puss
has always worked with my grandmothers cats. Her last cat was called Blue boy. very pretty blue fur.
Both my cats know their names. One comes every time whether I call him by name, make random sounds, or say nothing at all-- if he senses my presence within 100 yards, he comes to me. The other comes about half the time if I call her by name or say “kitty, kitty”… but her name*** is*** Miss Kitty.
Of course, both come instantly at feeding time.
Replying to my own post so I can add photos:
The late, great, Cirocco aka Rocky, Roc Roc, Rockrose, Roxy and many more, who not only answered to but approved of her many nicknames. I deduce this from the time she was steadfastly ignoring me until I coined her a new one, The Rockster.
Bonus cat I don’t know his name but I often meet him in the Botanical Gardens, which he treats as his personal fiefdom. He answers to “Hey Beautiful.”
I don’t think my cat Brrt knows her name, but when I get home from work and say “Where’s my kitty baby?” she comes to greet me. And she likes to hear me talk goo-goo when she is on my lap and purring.
I’ve always trained my cats to come running when I make a noise; it’s sort of a trill. My cat does not know her name as I never call her by it.
My more dog-like cat responds to his name. My more cat-like cat ignores his name, but will respond to trills some of the time.
Both of my cats know their own names, and they also know “good boy” and “good girl”. Plus, if I’m in the kitchen and yell “E-A-T”, they know it’s meal time and come running.