Ο επικεφαλής είναι εδώ.

Ο is the masculine singular definite article, so here it means the.

Greek uses the definite article much more regularly than English. In a sentence like this, where you mean a specific person — the leader / the person in charge — the article is normally required:

Ο επικεφαλής είναι εδώ. = The person in charge is here.

Επικεφαλής means something like leader, chief, head, or person in charge, depending on context.

It can behave like:

• a noun: ο επικεφαλής = the leader
• or an adjective: for example, ο επικεφαλής μηχανικός = the chief engineer

In your sentence, it is being used as a noun.

Επικεφαλής is a useful word because its form usually stays the same, while the article tells you the gender and number.

So:

• ο επικεφαλής = the male leader / the man in charge
• η επικεφαλής = the female leader / the woman in charge
• οι επικεφαλής = the leaders

So in your sentence, ο tells you the person is masculine.

Usually, επικεφαλής itself does not change form in everyday Modern Greek. The article is what shows the case.

For example:

• Ο επικεφαλής είναι εδώ. = nominative, because it is the subject
• Βλέπω τον επικεφαλής. = accusative, because it is the object

Notice that επικεφαλής stays the same, but ο becomes τον.

Είναι is the present-tense form of είμαι, which means to be.

Here, είναι means is:

• Ο επικεφαλής είναι εδώ. = The leader is here.

A useful thing to know: είναι can also mean are with they, so Greek uses the same form for:

• he/she/it is
• they are

Εδώ means here.

So the sentence structure is:

• Ο επικεφαλής = the leader
• είναι = is
• εδώ = here

Altogether: The leader is here.

Yes, Greek word order is fairly flexible.

Ο επικεφαλής είναι εδώ. is a very normal, neutral order:

• subject + verb + adverb

But you could also say:

• Εδώ είναι ο επικεφαλής.

That version puts more emphasis on here, as if answering Where is the leader?

So both are possible, but your original sentence is the most straightforward, neutral version.

In normal Greek, you would usually keep the article: Ο επικεφαλής είναι εδώ.

If you remove it, the sentence sounds less natural in ordinary speech and may feel more like:

• a headline
• a label
• or very compressed, telegraphic language

So for standard everyday Greek, use ο here.

A rough pronunciation guide is:

o e-pee-ke-fa-LEES EE-ne e-THO

A few helpful notes:

• επικεφαλής is stressed on the last syllable: -λής
• είναι is pronounced roughly EE-ne
• δ in εδώ sounds like th in this
• θ does not appear in this sentence

The stress marks in Greek show you where the voice stress goes:

• επικεφαλής
• είναι
• εδώ

It is generally neutral to somewhat formal. You often hear it in:

• workplaces
• organizations
• the news
• official situations

Depending on context, Greek might also use other words such as:

• ο αρχηγός = the chief / leader
• το αφεντικό = the boss

But επικεφαλής is a good standard word for the person in charge.

Not as written.

Because the sentence starts with ο, it refers to a masculine person:

• Ο επικεφαλής είναι εδώ. = The male leader is here.

For a woman, you would say:

• Η επικεφαλής είναι εδώ.

The word επικεφαλής stays the same; only the article changes.