What is Abraham's last name from the Old Testament?

Answer 1

Depending on where on earth one refers to, the practice of having a second or third name is of relatively recent advent in the span of world history.

In the times when Abraham lived, when the world was comparatively sparsely populated, it is almost a certainty that people of all ranks and walks of life had only one name, the name given by their parents or other authority figures (or assumed by themselves) who, themselves, also had only a single name. So, when we say, Abraham, we are referring to the only name by which he would have been known.

Although you might see reference to a person's lineage in the Old Testament--for example, one name as the "seed" or begatted of another--or the location where a so-named lived--such a with Saul of Tarsus--it would not be until a very very long time after old testament times that the practice of having a family name based on ancestry or location (or occupation and such) would come into existence. (In fact, the single name traditions still holds in some parts of the world, either be itself or coincidental with multiple-name practices. Some have even come up in news reports concerning the conflicts happening in the Middle East.)

In conclusion, there is no recorded "last" name for Abraham because "Abraham" was that patriarch's first, last, and only name.