Around 2002 / early 2003 Hasbro announced they were releasing an Anniversary figure in 2004 to commemorate 20 years. The prototype was revealed around July 2003, confirming this would be Optimus Prime, albeit without the trailer. Around December 2003, Takara released their version of the figure, MP-1 Convoy, designed by Hironori Kobayashi. It was not designated MP-01 as it was thought to be a one off release at the time.
For 8 years between 2003 and 2011, the initial line up saw 9 figures released (not counting exclusives) and out of those figures there were 5 original moulds. From 2011 onwards starting with the MP-10 Convoy "reboot", the Masterpiece line has become a standard toyline rather than a series of one off specials.
The figures have become smaller, less die-cast metal and recently are more and more cartoon accurate. At the time of writing ad after 14 years, the Masterpiece line looks to be far from over.
Click on the below images to view the corresponding article and translations of their extended bio's:-