Formulated in 19th century by German historians employed by Romanov dynasty, this theory states that Russia has been founded by Normans (Varangians) in 9th century AD and the first Russian ruler Rurik was a Varangian.
This theory became a mainstream in 20th century, moving into 21st century it is causing more and more questions. It’s main problem is that it is based on a single chronicle – The Tale of Bygone Years or The Primary Chronicle, whose authenticity is not proven.
The advent of modern DNA science allowed to test Rurik’s descendants DNA and according to Prof. Klyosov it showed that Rurik was not a Scandinavian, which effectively renders this theory obsolete.