The letter in question is the vowel "ы" -- a difficult-to-pronounce sound for nonnative Russian speakers which is usually transliterated simply as "y" in English. Zhirinovsky says he wants the letter removed from the Russian alphabet, calling it a "nasty Asiatic" import.
The vowel came to the Russian language from the Mongols, Zhirinovsky was quoted as telling the State Duma on March 12.
"Only animals make this sound, 'ы- ы,'" he said, adding that the regular "и" ("i") is enough for the Russian alphabet.
"Ы" doesn't exist in any other European language, argued Zhirinovsky. "This primitive, Asiatic sound is the reason people don't like us in Europe," he told lawmakers.
The politician seemed to have a longstanding issue with the "guttural" letter, which he claimed his son wasn't able to pronounce as a child.
"He once told me, 'Dad, dad, look, there's a 'мишка'," the Russian for "bear." "I thought 'What 'мишка'? A bear? But he meant 'мышка'," the word for "mouse."
Insulting rhetoric is nothing new for the leader of Russia's Liberal Democratic Party.
Last month, Zhirinovsky sparked outrage in Central Asia, saying the region's five republics should be grouped together as subjects of Russia.
The Almaty-born politician suggested the creation of the "Central Asian Federal Region" of Russia with a capital that should be known as "Verny."
"Verny" is Russian for "loyal," and also the old name for the Kazakh city of Almaty.
Straying beyond politics, Zhirinovsky suggested last month in the Duma that people should not kiss on the lips but only on foreheads.
He also advised disinfecting the skin before planting a kiss.
Beside the Russian and Belarussian Cyrillic alphabets, the letter "ы" also exists in most of the Turkic languages spoken in former Soviet republics, including Kazakh and Kyrgyz, which use the same alphabet.
The vowel is widely used in Kazakh and Kyrgyz, sometimes several times in the same word.
"Ырыс алды – ынтымақ," ("Yrys aldy - yntymaq") reads a Kazakh proverb, which translates as "There is no abundance without solidarity."
The letter "ы" also makes up most of the vowels of a well-known Kyrgyz saying -- "ырысы жоктун ырымы күч" ("yrysy zhoktun yrymy kuch") – that means "a person with no confidence believes in superstition."
-- Farangis Najibullah with contributions from RFE/RL's Kazakh and Kyrgyz services