Einar Eindridesson Thambarskelfir is an influential Norwegian noble and politician during the 11th century.

He headed the feudal lords in their opposition to Olaf Haraldsson.

Several references are made to him in Snorri Sturluson's Heimskringla.

His cognomen, Thambarskelfir, has two strongly differing explanations.

One is that it is derived from tomb, meaning shaking bowstring.

Thus, the name suggests a master of the longbow.

The other is that it is derived from tambr, meaning 'belly', and that it translates to 'wobbly belly', surely an unflattering reflection of his physical build.