It looks like Euphorbia corulescens..

I'm not up on the euphorbias, but Jay's ID is reasonable. Has it ever bloomed? Do you have a photo of the bloom? That would help confirm the ID.

I agree about the flowers. There are so many succulent Euphorbia species, that have evolved. Their

radiation is similar to the milkweed family Aclepiadoideae. Above Euphorbia coerulescens in flower. Below are other succulent Euphorbia.

@Jay 6a Chicago Yes, this is Euphorbia coerulescens.

Unfortunately, I do not have a flowering photo.

@Jay 6a Chicago I am saving this conversation so I can record the information about E virosa. I think E virosa has more of a candelabra appearance, with symmetrical arms around the spine, all with a similar growth pattern. E coerulescens looks more haphazard in its growth. Mine looks very haphazard in its growth pattern. To be honest, I need to find a different place for it because it is just too big for the narrow pot where I have it. It's dangerous putting that next to a bench.

@Jay 6a Chicago What kind of soil did you use for the E coerulescens that died out? Was it in a pot? Have you tried gritty mix?

I think I grew the Euphorbia corulescens in a gritty mix.