Narcís Casas was born on 27 November 1946 in Salt, Girona, into a humble family. He began his career in the world of motorcycling at a late age, as he spent his time working as a bricklayer. His passion for motorbikes led him to participate in several amateur enduro mountain climbs on the back of a Montesa Cota 247 Trial, achieving third place in the International TT of L'Espluga de Francolí, a fact that caught the attention of those present and led him to sign for Bultaco.

This allowed him to devote himself professionally to being a rider and to give up bricklaying. The following year, in 1971, he took part in the Spanish Championship riding a Bultaco Matador and sharing a team with Casimir Verdaguer, Bubú Casanovas and Toni Soler. That year he won the Dos Días de Madrid, came second in the Manresa race and ended the season by winning the race at l'Espluga de Francolí. Thanks to these victories he was proclaimed Spanish champion for the first time.

In 1972 he won the Spanish championship again, maintaining a great rivalry with his teammate Bubú Casanovas, who finally moved to the Montesa team. That year, he also won the bronze medal in the Six International Enduro Days in Czechoslovakia. In 1973 he won his third Spanish Championship in the last race after the retirement of Bubú Casanovas. In 1974 Casas and Casanovas suffered an accident when they collided head-on in a village, which caused injuries to the former's pancreas and abdomen, causing him to miss part of the season. Despite this, he managed to come back and finished second in the Spanish Championship.

Between 1975 and 1978 he won all the state championships and participated with outstanding results in various European races such as the ISDT on the Isle of Man or European Championship races in France, Germany, Poland, Sweden, etc. In 1979, Narcís Casas retired, although he continued to be actively involved in the world of enduro after being appointed Spanish national coach.

In this last period a great rivalry was forged with his teammate Josep Maria Pibernat and, as often happens in many cases, this evolved into a great friendship. So much so that in 1984 they both founded Gas Gas after the closure of the Bultaco factory and the failed attempt to revive the Italian brand SWM, eventually becoming a reference brand and producing 8,000 motorbikes a year. Because of his career and achievements (7 Spanish Championships and two gold medals in the Six International Enduro Days) Narcís Casas was nicknamed O Rei and is, without a doubt, a Clice legend.