From '38 to '58 the four big Buicks were Special, Century, Super and Roadmaster.
Special was the family sized Buick
Century was the same body with the more powerful engine (could make and hold 100 mph , the "century mark")
Super was a larger car with some nice appointments
Roadmaster was the larger car with top of the line appointments
In '59 they changed the names
Special became LeSabre
Century became Invicta (A LeSabre body with Electra engine and some up scale trim)
Super became Electra
Roadmaster became Electra 225.
'61 saw the Special name came back as a small Buick and the Skylark name as an up trim Special.
'61 was the last year of the separate Electra/Electra 225
In '63 the Invicta name was changed to Wildcat
For the early '70s Wildcat became Centurion.
The Invicta nameplate was only used from '59 to 63 and had not yet been reintroduced. (although there was talk of bringing th name back)
Sorry about that, I get talking Buick and I ramble.