Who is the author of the prayer "Nishmat kol chai" which is said on Shabbat, Yom Tov, and during the great Hallel at the Seder?
For an In depth discussion of this and many other such topics Listen to this Lecture http://www.yutorah.org/lectures/lecture.cfm/726352/Dr.%20Shnayer%20Leiman/Jewish%20Perspectives%20on%20Early%20Christianity:%20Toldot%20Yeshu
The lecture is an attempt to show that Toldot Yeshu is a much older text than it's first appearance in the 1700s. It explains there that when the Rashi says that the "Romani" have no language, have no alphabet, and other people write their books, he is referring to the idea that R. Shimon set up Latin as the Christian language, created the Christian Bible and otherwise created Christianity to make sure that Jews would not be drawn to it.
The Toldot Yeshu also claims that Nishmat Kol Chai was written by R. Shimon as well. (R. Shimon being Peter)
The Lecturer makes an empahtic point that this is just one Jewish tradition, but that there are others that disagree with it. His main focus was that the tradition is an old one.
The Machzor Vitri(A talmid of Rashi who lived during 11th - 12th century) Hilchos Peasach 66 brings down that it is a mistake to think that peter wrote nishmas kol chai and if one says this he will have to bring a chatas when the third bais hamikdash is built.
In Siddur Avodas Yisrael pg 206 he brings two commentaries on who the author is of nishmas kol chai one from the 15th century that the author was Rabbi Shimon Kipah. The other source says it was Rabbi Shimon ben Kipeh and some say Rabbi Shimon Ben Shetach.
Maybe Simon (Peter)?! See the whole conversation at http://www.globalyeshiva.com/forum/topics/curious-anecdote-discovered
or look at this: http://hebrewbooks.org/pdfpager.aspx?req=2585&st=&pgnum=285
cf. Mishna -Pesachim 10, 7