Borders of Slav territories under Samo, 631
The dates for Samo's rule are based on Fredegar, who says that he went to the Slavs in the fortieth year of Chlothar II (i.e., 623–24) and reigned for thirty five years. The interpretation that places the start of Samo's reign in the year of Fredegar's arrival has been questioned on the basis that the Wends would have most likely rebelled after the defeat of the Avar khagan at the First Siege of Constantinople in 626. The Avars first arrived in the Pannonian Basin and subdued the local Slavs in the 560s. Samo may have been one of the merchants who supplied arms to the Slavs for their frequent revolts. Whether he became king during a revolt of 623–24 or during one that inevitably followed the Avar defeat in 626, he definitely took advantage of the latter to solidify his position. A string of victories over the Avars proved his utilitas (usefulness) to his subjects and secured his election as rex (king). Samo went on to secure his throne by marriage into the major Wendish families, wedding at least twelve women and fathering twenty-two sons and fifteen daughters.
Each year, the Huns [Avars] came to the Slavs, to spend the winter with them; then they took the wives and daughters of the Slavs and slept with them, and among the other mistreatments [already mentioned] the Slavs were also forced to pay levies to the Huns. But the sons of the Huns, who were [then] raised with the wives and daughters of these Wends [Slavs] could not finally endure this oppression anymore and refused obedience to the Huns and began, as already mentioned, a rebellion. When now the Wendish army went against the Huns, the [aforementioned] merchant Samo accompanied the same. And so the Samo’s bravery proved itself in wonderful ways and a huge mass of Huns fell to the sword of the Wends.
The most well-documented event of Samo's career was his victory over the Frankish royal army under Dagobert I in 631 or 632. Provoked to action by a "violent quarrel in the Pannonian kingdom of the Avars or Huns" during his ninth year (631–32), Dagobert led three armies against the Wends, the largest being his own Austrasian army. The Franks were routed near Wogastisburg (Latin castrum Vogastisburg), an unidentified location meaning "fortress/castle of Vogast." The majority of the besieging armies were slaughtered, while the rest of the troops fled, leaving weapons and other equipment lying on the ground. In the aftermath of the Wendish victory, Samo invaded Frankish Thuringia several times and undertook looting raids there. The Sorbian prince Dervan abandoned the Franks and "placed himself and his people under Samo's realm".
In 641, the rebellious duke of Thuringia, Radulf, sought an alliance with Samo against his sovereign, Sigebert III. Samo also maintained long-distance trade relationships. On his death, however, his title was not inherited by his sons. Ultimately, Samo can be credited with forging a Wendish identity by speaking on behalf of the community that recognised his authority.