So who came up with those common name translations at first place?
Those common name translations are known as 音译 or transcription.
In Chinese, transcription is known as yīnyì (simplified Chinese: 音译; traditional Chinese: 音譯) or yìmíng (simplified Chinese: 译名; traditional Chinese: 譯名). While it is common to see foreign names left in their original forms (for example, in the Latin alphabet) in a Chinese text, it is also common to transcribe foreign proper nouns into Chinese characters.
Homophones abound in Mandarin Chinese, so most English words have multiple possible transcriptions. Since there are many characters to choose from when transcribing a word, a translator can manipulate the transcription to add additional meaning. The official reference guide for transcription is Names of the World's Peoples (世界人名翻译大辞典), published by the Xinhua News Agency.
Chinese is written with monosyllabic logograms which may not correspond to the syllables in the foreign words. For example, a word of three syllables will be transcribed into at least three Chinese characters, in most cases three meaningful verbal units. Transcriptions into other Chinese dialects such as Cantonese will differ from Mandarin transcriptions, since transcription based on one dialect may not sound close to the original when pronounced with another dialect.
Names can be transcribed differently between the official transcription standards used within each of the different Chinese speaking regions. For example, US President Barack Obama's surname is rendered:
欧巴马 / 歐巴馬 Ōubāmǎ (Official translation)
奥巴马 / 奧巴馬 Àobāmǎ (used mostly in mainland China, Hong Kong, Macau, Malaysia and Singapore)
When transliterating foreign names whose pronunciation does not correlate to the spelling (especially in Russian names), Mainland China tends to preserve the original pronunciation, while Taiwan tends to transcribe along the spelling. For example, Putin, the former Russian president, is called 普京 （pujing）in Mainland China and 普廷 （puting）in Taiwan. In this case, when
i, its pronunciation will become
And why do they sound not similar to their English pronunciation?
The IPA pronunciation of "Robert Wilson" is /ˈrɒbərt ˈwɪlsən/
Referring to the English-into-Chinese transcription table from the semi-official Names of the World's Peoples (世界人名翻译大辞典), compiled by the Proper Names and Translation Service of the Xinhua News Agency:
/ˈrɒbərt ˈwɪlsən/ is transcribed as "罗伯特·威尔森 (森 not 逊)"
The person who came up with the original transcription may not be able to follow the pronunciation close enough resulting in some Chinese words sounding quite different from the original pronunciation. But since it has already become a standard, people tend to follow it and not come up with new things.
Notice also in the table that 若,维,欧,波 have already been used elsewhere, so changing one will affect the other.