Ahmed Ibn Fadlan was in fact a real historical figure, he lived in the early 10th century and was sent in 922 as an ambassador to the King of the Bulgars by the Caliph of Baghdad. During this posting he encountered the tribes of the Rus, who roamed far and wide as traders.
The chronicle that he wrote, The Risala contains much information on the physical and cultural make-up of 10th century Rus society, as well that of other peoples he met on journeys for the embassy . He was an astute observer, and his works are taken to be primary historical sources, albeit somewhat tainted by predudice against the more 'rustic' tribes.
Michael Crichton used Ibn Fadlan (played by Antonio Banderas) and some of the details in The Risala to flesh out his film The Thirteenth Warrior. Indeed it's probably through the use of the Risala that so many of the incidental details of the daily life of the Vikings appear authentic.