The Strange courier, as his name suggests, is a strange man who waited next to the bridge in Lumbridge during the events of 2010 Easter event. The player, once finished managing the factory and helping the Easter Bunny, was directed to deliver a crate of goods to the suspicious fellow.
If the player has done up to at least Mourning's Ends Part I in the Elf quest series prior to meeting him, the player will identify him instantly as an elf. This elf is collecting goods from the Easter Bunny to celebrate the rebirth. He also explains to players what elves do on Easter, and why the holiday is important to them.