Baron Lenshire is an NPC about which comparatively little is known. He is or was a noble of the City of Jhelom, was said to be an ally and/or friend of Lord Blackthorn before the latter turned evil, and is said to have a semi-credible, if convoluted, claim to the throne of Britannia. He appears to make a living doing some kind of trading, and has had issues with piracy, and with a warlord named Belo Ondariva who hailed from the Land of the Feudal Lords (which eventually became the Tokuno Islands. (There is some dispute, it should be noted, if Belo Ondariva's existence is "official" fiction or is "player" fiction that was adapted by the manufacturer.)
The Baron has been especially referred to in events on the Europa and Pacific Shards.
It has gotten extremely difficult to sort out facts about the Baron are derived from official game-wide fiction, from official but Shard-specific fiction as written by Seers and Event Moderators, and from non-official player fiction.
In some cases, these EM interpretations have even led to items such as the Lenshire Clan Tabard.
For more, visit the following links:
http://www.uoforums.com/twilight-fellowship/53570-tokuno-history.html (This appears to be shard-specific player fiction)
http://www.uoforums.com/uo-event-forum/55877-faction-invasions-who-what-when-where-why-4.html (Warder Dragon of Baja mentions Baron Lenshire's claim om the throne)
http://crwth.org/~crwth/uo/riddle.html (From the Pacific shard, but it's unclear if this refers to a player event or an EM or Seer event)
http://vboards.stratics.com/showthread.php?t=52094 (relates to Europa)