There are many versions of the origin of the Rurik dynasty. Any of them can be called believable.
One version is the history of the origin of the Rurikovich clan from the Varangian tribe.
In the north of our future country, in the city of Slavensk lived the tribe of the same name of the glorious. The riches of the Varangians attracted the wealth of their city. And so, in order to get rid of their attacks, at the call of the elder of Gostomysl, Slaven gathered for a campaign. Having defeated and drove the Varangians overseas, the Slavs elected Gostomysl as their prince.
To avoid further war with the Varangians, the prince decided to give his daughter Umila to the Varangian prince. From their marriage a son was born, who was named Rurik.
After the death of Prince Gostomysl, the Slavs began feuds and a struggle for power. To rule the world, it was decided to call on the principality of Rurik, the grandson of Gostomysl. So they assume, and the history of Russia began, and the Rurik dynasty appeared.