Björn Järnsida (Ironside), was a Viking raiding France in the 9th century. According to the old sagas he was the son of Ragnar Lodbroks and participated in Ragnars siege of Paris. The sagas also say that Björn got the name Ironside because he was never injured in battle. (Picture from the TV show Vikings).
Halfdan Ragnarsson was a Viking leader and a commander of the Great Heathen Army. According to the tradition recorded in the Norse sagas he was one of the sons of Ragnar Lodbrok, and his brothers included Björn Ironside, Ivar the Boneless, Sigurd Snake-in-the-Eye and Ubba. He was the first King of Jórvík and also claimed the Kingdom of Dublin. He died at the Battle of Strangford Lough in 877 trying to press his Irish claim.
The Great Heathen Army (OE: mycel heathen here), also known as the Great Danish Army or The Great Viking Army, was a combined Viking force originating in Denmark and southern Sweden that invaded England in 865 AD.
Ragnar Lodbrok met his end in England when he was captured by his long-time nemesis King Ælla of Northumbria who threw him into a pit of snakes. The Saga Ragnarssona þáttr (The Tale of Ragnar’s Sons) relates that it was this act that caused the Great Heathen Army to invade England at the behest of Ragnar’s children who demanded revenge for the death of their father.