ThinkPad R series
The R series was developed as a direct successor of the discontinued 300 series. Other than lacking 2-in-1 convertible models, it served the same purpose as the 300 series did.
From the R50 onward, the R series turned into what was basically a duplicate of the T series that was thicker, and with less features. It also had a less luxurious construction, as its lid was not rubberized like the T series' lid was. Another major difference was that it had FireWire, which was something that the T series did not have until the introduction of the T61.
Eventually, the R series was discontinued and was indirectly succeeded by the SL series. However, Lenovo has bought it back to serve as a more luxurious sidegrade for the E series. The new R series now features an identical construction to its E series counterparts, and has aluminium lids to identify itself as the luxury counterpart of the E series.