Learn Hardcore Russian: Я читаю биографию известного инженера и смотрю его портрет на первой странице. - I am reading the biography of a famous engineer and looking at his portrait on the first page.

Биография is a feminine noun ending in -я. In the sentence, it is the direct object of the verb читаю (I am reading), so it must be in the accusative case:

Nominative (dictionary form): биография – a biography
Accusative singular: биографию – a biography (as the thing being read)

For most feminine nouns ending in -я, the accusative singular ends in -ю:

история → историю (history)
компания → компанию (company)
биография → биографию (biography)

Why is it известного инженера and not известный инженер?

The phrase биографию известного инженера can be broken down like this:

биографию – the biography (accusative)
известного инженера – of a famous engineer

In Russian, “biography of someone” is expressed using the genitive case (“whose biography?” = кого? чего?).

инженер (nominative) → инженера (genitive singular)
The adjective must agree with the noun in gender, number, and case, so:
- известный (masc. nominative) → известного (masc. genitive singular)

So the whole phrase is:

биографию (кого?) известного инженера
the biography (of whom?) of a famous engineer

If you said известный инженер in this position, it would sound like the engineer is the subject (nominative), which is wrong for this structure.

Why is инженера in the genitive case here? In English we just say “a famous engineer” after “biography.”

In English, “a biography of a famous engineer” feels like a simple noun phrase.
In Russian, the relationship is more explicit: “biography of whom?”

The noun биография often takes a genitive complement:

биография Пушкина – the biography of Pushkin
биография этого учёного – the biography of this scientist
биография известного инженера – the biography of a famous engineer

So, инженера is in the genitive case because it answers the question кого? (of whom?).

Why does портрет stay as портрет? Why not something like портрета?

Портрет is a masculine inanimate noun.

In Russian, for masculine inanimate nouns, the accusative singular form = the nominative singular form:

Nominative: портрет – portrait
Accusative: портрет – portrait (as direct object)

So in смотрю его портрет (“I am looking at his portrait”),
портрет is the direct object in the accusative, but its form does not change.

Compare:

Masculine animate:
- Я вижу инженера – I see the engineer.
  (accusative = genitive)
Masculine inanimate:
- Я вижу портрет – I see the portrait.
  (accusative = nominative)

What does его mean here, and how do we know it refers to the engineer?

Его can mean:

his (possessive)
him (as a pronoun in object position)

In this sentence, in смотрю его портрет, it means his:

его портрет – his portrait

How do we know it refers to the engineer?

The only masculine singular person mentioned in the sentence is известный инженер.
It is natural to assume его refers to that noun: the portrait of that famous engineer whose biography I am reading.

There is a small potential ambiguity (it could be “someone else’s portrait” in some contexts), but in normal reading, the default interpretation is that его refers to известный инженер.

Why is it на первой странице and not в первой странице?

Russian uses different prepositions for location:

на = on (a surface, or metaphorical “on”)
в = in, inside

A страница (page) is treated as a surface (you look at what is printed on it), so Russian uses на:

на странице – on the page
на первой странице – on the first page

Other examples:

на доске – on the board
на столе – on the table
на обложке – on the cover

В странице would sound wrong; it would suggest something physically inside the page material.

Why is it первой странице and not первая страница?

The base forms are:

первая страница – the first page (nominative)
Feminine adjective: первая
Feminine noun: страница

But in на первой странице, both words are in the prepositional case, used after на when indicating location (“on where?”):

Nominative: первая страница
Prepositional: на первой странице

The endings for feminine singular in the prepositional are usually:

Noun: -е → страница → странице
Adjective: -ая → -ой → первая → первой

So:

на (какой?) первой (чём?) странице – on the first page

Why are читаю and смотрю both in the present tense imperfective? Could you use a different aspect?

Читаю (I am reading) and смотрю (I am looking at / watching) are both:

Present tense
Imperfective aspect

Imperfective here expresses an ongoing action or what you’re doing right now:

Я читаю биографию... и смотрю его портрет...
I am reading the biography... and looking at his portrait...

If you changed the aspect:

Я прочитал биографию – I (have) read/finished the biography (perfective, past, completed action)
Я посмотрел его портрет – I (have) looked at his portrait (already) (perfective, past)

In the original sentence, we want a simultaneous, in-progress description, so the present imperfective is exactly right.

Could you leave out я and just say Читаю биографию... и смотрю его портрет...?

Yes, you could.

In Russian, the verb ending already encodes the subject, so the pronoun я is optional in many contexts:

Я читаю. = Читаю. – I am reading.
Я смотрю. = Смотрю. – I am looking / watching.

In neutral written style, including я is very normal and clear.
In informal speech or when the subject is obvious from context, Russians often omit я.

Is there any way to see from the Russian that it means “the biography” and “the portrait” and not “a biography / a portrait”?

Russian has no articles (a, an, the). The words:

биография
портрет

and their forms (биографию, портрет) on their own do not tell you whether the meaning is “a” or “the”.

You rely on context:

If the speaker is talking about a specific engineer whose biography and portrait are known from context, you translate:
- Я читаю биографию известного инженера и смотрю его портрет...
- I am reading the biography of a famous engineer and looking at his portrait...
Whether you choose “a” or “the” in English depends on what sounds natural given the broader conversation, not on any formal marker in Russian.

What is the difference between известный and знаменитый? Could we say знаменитого инженера instead?

Both mean roughly “famous / well-known”, but with slightly different flavors:

известный – known, well-known, recognized
(can be slightly more neutral or technical)
знаменитый – famous, renowned
(often feels a bit stronger or more “celebrity-like”)

In this sentence, both are grammatically fine:

биографию известного инженера – biography of a well-known engineer
биографию знаменитого инженера – biography of a famous / renowned engineer

The choice is more about style and nuance than grammar.

What is the difference between его and своего here? Could we say смотрю свой портрет?

Yes, you could say смотрю свой портрет, but the meaning changes.

его портрет – his portrait (of some male person mentioned or understood from context)
свой портрет – one’s own portrait

Свой is a reflexive possessive; it usually refers back to the subject of the clause:

Я смотрю свой портрет. – I am looking at my own portrait.
Он смотрит свой портрет. – He is looking at his own portrait.

In the original sentence, его портрет points to that engineer (not to “I”).
If you changed it to свой портрет, it would mean that I am looking at my own portrait, which is a different situation.

Could we use а instead of и here: ...биографию известного инженера, а смотрю его портрет...?

You could, but it would change the meaning.

и = and, simply adds one action to another:
- читаю ... и смотрю ... – I am reading ... and (also) looking ...
а often suggests contrast or “on the other hand”:
- читаю биографию, а смотрю его портрет
  sounds like you’re contrasting reading the biography with looking at the portrait, which is odd here.

In this sentence, we just want to say that both actions are happening together, so и is the natural choice.