Keke had a relatively late start to his F1 career, debuting at the age of 29 after stints in the Toyota Atlantic series, Formula Vee, and a successful stint in Formula 2, then the "feeder" to F1. He debuted with the underpowered Theodore team in 1978 and won a non-championship race that season in just his second race with the team, emerging victorious after many of the big names dropped out. Rosberg wasn't able to qualify for a race afterwards, and was signed by another uncompetitive team, ATS for 3 races after the Theodore team scrapped the unreliable car design. He returned with Theodore after they borrowed chassis from the Wolf formula 1 team, but these failed to work with the team, and returned to ATS to end the season.
He emerged with the Wolf team midway through 1979, but it was having problems staying afloat, and Keke had problems finishing races. Rosberg had to change teams again when they left F1, and signed with Emerson Fittipaldi's racing team. He had his first two point-scoring results in 1980 but often failed to finish or qualify, it was even worse in 1981 when he failed to score again.
Despite this, Williams had an interest in Keke in 1982 with the retirement of previous World Champion Alan Jones leaving a spot open. Given a competitive car, Keke was a revelation that year. Rosberg consistently scored points and earned his first victory at Dijon-Prenois late that year. Rosberg's season came in a year where no driver won more than two races and his consistency won Rosberg an unlikely championship.
With the developments of Alain Prost, Nelson Piquet, and the re-emergence of Niki Lauda, Rosberg didn't come close to winning another title but continued his consistent driving with Williams, when the car wasn't breaking down, for 3 more seasons before retiring with a productive year at McLaren in 1986.
The original "Flying Finn" later spent a long time managing future world champion and fellow Finn Mika Hakkinen. His son Nico has proved to be a good racer himself and has spent time test driving for Williams.