Jarl Sigvaldi was the son of Strut-Harald the Jarl of Skåne and the brother of Thorkell the Tall (Torkjell Høge). He succeeded Palnatoke as the chieftain of the Jomsvikings, but he proved more wise than brave.
In order to win Astrid, the daughter of the Wendish chieftain Burislav, he promised to liberate the Wends of the tribute they had to pay to the Danes. He fulfilled his promise by sailing to Zealand where he sent the message to Sweyn Forkbeard that he had important tidings, but had fallen ill and could not come in person to bring them to him. As Sweyn was curious, he went aboard Sigvaldi's ship and was captured by the Jomsvikings. To be liberated the Danish king had to grant independence to both the Jomsvikings and to the Wends, in addition to paying a king's ransom. Svein also had to marry Gunhild of Wenden, daughter of Burislav and Burislav married Sweyn's sister Tyri.
At the funeral of his father, Strut-Harald, Sigvaldi was advised by Sweyn to attack Norway and to depose Haakon Jarl. This promise led to the Battle of Hjörungavágr in 986, from which Sigvald fled with disgrace.
In 1000, Sigvaldi proved to be treacherous at the Battle of Svolder, by luring Olaf Tryggvason to the battle and by deserting him in the heat of battle.
There is no record of him after the Battle of Svolder. However, his brother Thorkell's invasion of England in 1009 was allegedly intended to avenge Sigvaldi's death
I dont know if Egil Skallagrimson and Jarl Sigvaldi ever meet but here they at least pose for this picture;)