Rasputin was siad to have been very well endowed, some 13 inches. However, there have been many rumors and legends concerning what became of his penis, and it is hard to say if the object in the jar is really his. In fact, an object long represented to be Rasputin's penis turned out to be someting else entirely--
Consider this article:
http://www.themightyorgan.com/features_rasputin.html
Or this one, which regards the rumors of the severing of the penis to be part of a fanciful embellishment of the story of his murder:
http://www.rotten.com/library/bio/historical/rasputin/
Other stories about Rasputin's penis have described it as being more slender then the object in the jar, although quite long.
A lot of stories about Rasputin are hard to belive, but are likewise difficult to refute. He had formed a sort of religious cult centered around sex, the theory being that by deliberately sinning through debauchery, he could actually bring people closer to God. His ability to stop the bleeding of the Czar's hemopheliac son of course gave credibility to claims of being a saint. He certainly was a promiscuous womanizer, and may well have had a big dick. Then again, there may have been some exageration on the part of those who idolized him (just as groupies seem to attribute vast sexual prowess to almost every rock star). Either way, 30 cm (11.8 inches) is certainly possible, as I've met a few guys in this range.