Lost Nuances in 'Ivan the Terrible'
In Japanese: 'Ivan the Thunder Emperor'.
... ロシア語の渾名「グロズーヌイ」 (Грозный) は「峻厳な、恐怖を与える、脅すような」といった意味の形容詞で、この単語自体に「雷」という意味はない。類語に「雷雨」ないし「ひどく厳格な人」という意味の名詞「グロザー」（гроза）があり、この単語との連関から「雷帝」と和訳された。英語ではたんに「恐ろしいイヴァン」（Ivan the Terrible）と訳しているが、これは「雷のような畏怖すべき威厳のあるさま」を表している原語のニュアンスを損なっている。
The Russian epithet 'Grozny' is an adjective; the word means 'stern, terrifying, and menacing', but does not by itself refer to 'thunder'.
There is however a quasi-synonym called 'groza', a noun whose meaning ranges from "thunderstorm" to "a severely strict person". The Japanese translation of Ivan's nickname is derived from this relationship in meaning with 'groza', thus Ivan's nickname is rendered 'Thunder Emperor'. In English however, Ivan is simply referred to as 'Ivan the Terrible', but this translation loses the original nuance of 'groza', i.e. 'one whose dignified presence evokes awe and fear, like thunder'.
Ivan IV of Russia, who is known to English speakers as 'Ivan the Terrible', is instead known to the Japanese as 'Ivan the Thunder Emperor' (イヴァン雷帝).
To English speakers, 'Thunder Emperor' comes off as a hilarious-sounding nickname for a monarch. But connotation-wise, the title is more accurate than just 'The Terrible'. (Personally, I prefer 'Ivan the Terrible' over 'Ivan the Thunder Emperor'. The latter translation sounds stilted.)