I live in South Carolina. Can you suggest the hardiest perennial that can handle poor drainage clay soil, hot, humid and full sun? Thanks

Hyloptelephium, may be sold as sedum, such as Autumn Joy, that one is bulletproof and easy to propagate if you want more, while no nasty self sowing habits.

There's plenty of stuff.
Like Helianthus angustifolius, & Hibiscus coccineus, & Solidago...

We actually need you to tell us how tall... The 3 plants I listed may get 6 foot tall...

We need information about what bloom season is important...

And... while the 3 I listed are really good for the wildlife garden... are there any birds and pollinators that you are especially interested in attracting?

You can probably find seed for echinacea, rudbeckia, and asclepias tuberosa... They should grow easily if you till.

My goal is always to attract pollinators, incorporating lots of color, mixing different Perennials is fun, would love blooms from spring to early fall..as far as height..these are small areas so no more than 3ft..I'm sure I'm asking for a miracle.

Full Sun..

The biggest challenge is poor draining clay soil.

well, I thought I was limited to one hardiest perennial. But all of what stone suggests now adds to the mixture you'd like. Mostly summer-fall bloomers, we need to think of spring, and you need to watch height on some. Joepyeweed for example would love poorly drained but even Little Joe is a good 4 feet tall for me.
How poorly drained? Like a low area staying too wet ? Clay in itself isn't all bad.
Spring bloom makes me think of woodland ephemerals, or annuals.

Black and blue salvia would be great, I 'think' the one I have is black and blue, aka species guaranitica? Constant bloom, bumblebees and hummers love it.

Also consider canna and lantana, Vernonia.
Please post a picture of area.

Clay is easy...

I'm in the sandhills, with beach sand 200 ft deep... kinda difficult to grow much in that...

How about ruellia... I'm partial to 'ragin cajun'.

I really like salvia, but not sure about ability to survive winter in wet clay.

Check out turmeric, curcuma longa... The plant we make curry from...

Are you still here?
Thought of another great plant...
Maybe try Malvaviscus...

There's a caveat...
If you live upslope it will be fine...
If you live downslope (frost pocket), Might be difficult to get through the late frosts...

The thing to remember about clay?
It holds moisture ands nutrients...
You want to get out there with a shovel while the clay is moist enough to turn...
I always prefer to dig the clay in the winter, but we've been lucky this Spring... I was turning some clay in town last week... And planting some that had been resting since being turned a month or two ago.

Both operations went fine.