Roboforce was a relatively small Space theme that came out in 1997. It was the last "human" Space faction before the Dark Ages of Space history (between Insectoids in 1998 and Mars Mission in 2007), and consisted of a total of four sets. Coming on the heels of the rather larger Exploriens theme in 1996, the Roboforce were something of a "one schtick" theme: robots. Despite that, and the corresponding poor press that they seem to have had, the Roboforce had some excellent minifigs, and although I've never managed to get my hands on any of the sets, I do have two figs, one of each main variety: red/orange and yellow/neon green.
The yellow fig was something I decided to get because of an assortment of pieces that I got used for Christmas around 2004 (I'm not positive of the exact year), together with a bunch of pieces that seem to have come with one of the yellow Roboforce sets. The red fig was also a Bricklink build, though he came piecemeal over the course of a year or two, instead of as a single unit. Consequently, he does not have a "standard" Roboforce head, as the yellow ones does.