Illinois Central 121 (IC #121) was a diesel streamliner built in 1936 by Pullman-Standard and powered by Electro-Motive Corporation, which was used by the Illinois Central Railroad on the Green Diamond. Its fixed five-car consist was also the end of an era; the popularity of the early streamliners was their undoing, because the trains could not be lengthened or shortened to handle varying loads. It was the last streamliner built with the power car articulated with the train; future streamliners featured a matched but separable locomotive. The train was painted in a two-tone green livery, "Cypress Green" on the nose and below the window sills with "Cedar Green" above, separated by an aluminum strip. Extensive aluminum trim was applied.