der Iraker
Iraqi
A male citizen or resident of Iraq.
Der Arzt, der mich behandelt hat, ist Iraker.
The doctor who treated me is Iraqi.

Iraqi
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Iraqi
A male citizen or resident of Iraq.
Der Arzt, der mich behandelt hat, ist Iraker.
The doctor who treated me is Iraqi.

The masculine term for inhabitants is often formed by adding the ending '-er' to the name of the country (Irak). This pattern applies to many countries, e.g. 'Italien' (Italy) → 'Italiener' (Italian man).
Mein Nachbar ist Iraker und lebt seit zehn Jahren in Deutschland.
My neighbor is Iraqi and has lived in Germany for ten years.
'Iraker' (Iraqi) is a noun and is always capitalized. After the verb 'sein' (to be), it can stand with or without an article, though the form without an article is more common.
Er ist Iraker.
He is Iraqi.
To describe things that come from Iraq or relate to the country, you use the adjective 'irakisch' (Iraqi). This adjective is placed before a noun and declined.
Ich mag die irakische Küche sehr.
I really like Iraqi cuisine.
Arab / Arabian
'der Araber' and 'der Iraker' can both describe people from the Middle East, but they do not mean the same thing. 'der Iraker' describes a man from Iraq or a citizen of Iraq. 'der Araber' is broader: it is about Arab origin, the Arabic language, or an Arab country. An Iraqi can be Arab, but not every Arab is Iraqi. The words can be confused if you do not clearly separate origin, language, and nationality.

Der neue Kollege ist Iraker und kommt aus Bagdad.
The new colleague is Iraqi and comes from Baghdad.
Mein Nachbar ist Araber und spricht zu Hause Arabisch.
My neighbor is Arab and speaks Arabic at home.