Why the -ом on the first name and -ым on the last name?

The last names with this paradigm (ending in -ов, -ев, -ёв, -ин, -ын and their female counterparts) developed from posessive adjectives and decline like those, though keeping the old short form paragigm: Коровина, Коровину rather than **Коровиного, **Коровиному.

Actually, Коровин is a contraction of Коровин сын: a son of a person named, dubbed, nicknamed, or otherwise yclept корова (cow).

Until quite recently, it was the way to write the patronymics (Иван Петров сын Сидоров), and it's still used in Bulgarian.

Note that this paradigm is only valid for last names of this origin.

Names originated from other languages (Асприн, Толкин etc.) are declined as nouns (Асприном, Толкином).

Russian names which have not originated from posessive adjectives (Литвин, Мордвин) also decline as nouns (Литвином, Мордвином). However, the names' origins in this case are not obvious from sg. nom., so these last names can decline as posessive adjectives as well, and only the name bearer may know the right form.

The name of Ivan Ivanovich Sakharine, the antagonist in "Tintin's adventures", is declined Сахариным, not Сахарином in Russian translation (though both versions are grammatically possible). It's believed it should be an old aristocratic family name originated from the word сахар (sugar), not quite a recent nick originated from сахарин (saccharin).

Why the -ом on the first name and -ым on the last name?

The last names with this paradigm (ending in -ов, -ев, -ёв, -ин, -ын and their female counterparts) developed from posessive adjectives and decline like those, though keeping the old short form paradigm: Коровина, Коровину rather than **Коровиного, **Коровиному.

Actually, Коровин is a contraction of Коровин сын: a son of a person named, dubbed, nicknamed, or otherwise yclept корова (cow).

Until quite recently, it was the way to write the patronymics (Иван Петров сын Сидоров), and it's still used in Bulgarian.

Note that this paradigm is only valid for last names of this origin.

Names originated from other languages (Асприн, Толкин etc.) are declined as nouns (Асприном, Толкином).

Russian names which have not originated from posessive adjectives (Литвин, Мордвин) also decline as nouns (Литвином, Мордвином). However, the names' origins in this case are not obvious from sg. nom., so these last names can decline as posessive adjectives as well, and only the name bearer may know the right form.

The name of Ivan Ivanovich Sakharine, the antagonist in "Tintin's adventures", is declined Сахариным, not Сахарином in Russian translation (though both versions are grammatically possible). It's believed it should be an old aristocratic family name originated from the word сахар (sugar), not quite a recent nick originated from сахарин (saccharin).

Why the -ом on the first name and -ым on the last name?

The last names with this paradigm (ending in -ов, -ев, -ёв, -ин, -ын and their female counterparts) developed from posessive adjectives and decline like those, though keeping the old short form paragigm: Коровина, Коровину rather than **Коровиного, **Коровиному.

Actually, Коровин is a contraction of Коровин сын: a son of a person named, dubbed, nicknamed, or otherwise yclept корова (cow).

Until quite recently, it was the way to write the patronymics (Иван Петров сын Сидоров), and it's still used in Bulgarian.

Note that this paradigm is only valid for last names of this origin.

Names originated from other languages (Асприн, Толкин etc.) are declined as nouns (Асприном, Толкином).

Russian names which have not originated from posessive adjectives (Литвин, Мордвин) also decline as nouns (Литвином, Мордвином). However, the names' origins in this case are not obvious from sg. nom., so these last names can decline as posessive adjectives as well, and only the name bearer may know the right form.

The name of Ivan Ivanovich Sakharine, the antagonist in "Tintin's adventures", is declined Сахариным, not Сахарином in Russian translation, though both versions are possible, because it's believed it should be an old aristocratic family name originated from the word сахар (sugar), not quite a recent nick originated from сахарин (saccharin).

Why the -ом on the first name and -ым on the last name?

The last names with this paradigm (ending in -ов, -ев, -ёв, -ин, -ын and their female counterparts) developed from posessive adjectives and decline like those, though keeping the old short form paragigm: Коровина, Коровину rather than **Коровиного, **Коровиному.

Actually, Коровин is a contraction of Коровин сын: a son of a person named, dubbed, nicknamed, or otherwise yclept корова (cow).

Until quite recently, it was the way to write the patronymics (Иван Петров сын Сидоров), and it's still used in Bulgarian.

Note that this paradigm is only valid for last names of this origin.

Names originated from other languages (Асприн, Толкин etc.) are declined as nouns (Асприном, Толкином).

Russian names which have not originated from posessive adjectives (Литвин, Мордвин) also decline as nouns (Литвином, Мордвином). However, the names' origins in this case are not obvious from sg. nom., so these last names can decline as posessive adjectives as well, and only the name bearer may know the right form.

The name of Ivan Ivanovich Sakharine, the antagonist in "Tintin's adventures", is declined Сахариным, not Сахарином in Russian translation (though both versions are grammatically possible). It's believed it should be an old aristocratic family name originated from the word сахар (sugar), not quite a recent nick originated from сахарин (saccharin).