Longest journey by motorcycle (individual)
Who
Emillio Scotto
What
735000 kilometre(s)
Where
Argentina (Buenos Aires)
When

Emilio Scotto of Buenos Aires, Argentina completed the longest ever journey by a motorcycle, covering over 735,000 km (457,000 miles) and 214 countries and territories, from 17 January 1985 to 2 April 1995.

This is classed as a single journey because he didn't return to his country of departure until the end.