In its more modern, colloquial translation, the word "Riddarinn" can simply mean "horse rider", or "Horseman". Older versions of the word "Riddari" directly implies a knight, more or less a knight on horseback, or "Mounted warrior".
The ancient Norse were no strangers to horses, and usually used them for transporting and trading goods. The Icelandic Horse breed is one of the few horse breeds in the world capable of five gaits, as opposed to the usual three, and were brought to the Island as early as 875 AD. However, in 982, the Icelandic parliamant known as the Alingi (Althing) began to prohibit the importing of horses to the island.