Why are there letters which look similar but are pronounced differently between the English alphabet and Russian Cyrillic?

Question

Gadling teaches you to read the Cyrillic alphabet in 5 minutes mentions that there's some letters in Cyrillic that look like letters in the English alphabet, but their pronunciation in Russian is different to the similar looking letter in English:

3. Some letters ... look familiar but don’t sound like their English counterparts. The Russian letter “H” makes the “N” sound, “y” makes the English “oo” sound, and “B” sounds like the English “V.” This letter, И, which looks like a backwards “N”, makes the “short i” sound, as in the English word “pin.” The Russian letter “Я” sounds nothing like [its] mirror image in English. Instead, it makes a “ya” sound, as in “yacht.”

Why is this the case?

I tried looking it up, but only found sites with user generated content discussing the issue.

Answer 1

Cyrillic alphabet was developed in what is modern Bulgaria based on Greek alphabet, so:

• В was modeled after Greek Β (beta). This was originally pronounced [b] in ancient Greek but in modern (and medieval) Greek it is weakened to [v]

• Н, which originally looked N, was modeled after Greek Ν (nu)

• И, which originally looked Н, was modeled after Greek Η (eta). In ancient Greek this was pronounced similarly to English [h], but the sound was lost by the 6th century BCE and character was then repurposed for an [i] sound, as in contemporary Greek.

• У was originally part of a digraph ОУ, which was modeled after Greek digraph ΟΥ (omicron ypsilon) which the Greek used to denote [u]

• Я was originally written Ѧ and denoted a nasal sound similar to final sound in French fin which later changed to modern [ja] in Russian and Russian recension of Church Slavonic.

Answer 2

Russian.SE is filling with the user's contents too, I don’t see anything wrong with it. But such a content has to be effectively verifiable.

Another question closely related to the OP question: Why does the Cyrillic alphabet has the order A,B,V,G and pronounced like А, В, V, G(goo) ?

Please read/search/verify following keywords:

         Egyptian         -->  pictograms
        hieroglyphs
             |
         Phoenicia             http://phoenicia.org/tblalpha.html
     (about 1700 B.C.)    -->  pictures for syllables
             |
            ...
             |
     (about 1300 B.C.)    -->  pictures for the initial consonants
             |
         Phoenicia 
             |
         spread to
          /       \
         /         \
  across Asia    Greece   -->  + pictures for vowels
        \         / |  \
         \       /  |   \
           Russia   |   Rom  --> Latin
             |      |    |
             |      |  some
             |      |  changes ------ France, England, America, ... 
             |      |                            |
             А      А                            А
             |      |                            |
             |   (200 A.D.)                      |
             Б  B-sound dropped,                 B
             |   ┌ Beta sounded as V             |
             |  ┌┘                               |
             В ┘                                 V
             Г      Γ                      C (sounded as K) replaced G
             Д      Δ                            D
            ...    ...                          ...
             Н      Η(eta) sounded as i in pin   I
             |                                   |
     (replaced at XII c.)                        |
             И      |                            I
             |      |                            |
            ...    ...                          ...
             |      |                            |
             П      Π                            P
             Р      Ρ                            R
             |
       new consonants
       to represent 
       sounds (ж,ч,ш,щ,ц)
              |
             ...
              |
              Я is a modification of the Alpha. 
                The right line is made vertical
                and the left line is curved.