Question: Which Earl allegedly founded the English colony granted land by the Byzantine Emperor Alexius I Comnenus?

Context articles: Játvarðar Saga
Euthymios Zigabenos
Alexios IV Angelos
New England (medieval)
Alexios Komnenos (co-emperor)
Basil the Physician
Theodora Angelina (daughter of Isaac Komnenos)
Alexios II Komnenos
Perama, Ioannina
Alexios I of Trebizond

The Játvarðar Saga (in full Saga Játvarðar konungs hins helga), is an Icelandic saga about the life of Edward the Confessor, King of England (1042–1066).
 It was compiled in the 14th century, in Iceland, using a number of earlier English sources as well as the French "Chronicon Universale Anonymi Laudunensis" (or a source common with it).
 It was translated into English in 1894 by G. W. Dasent.
 Among the various details contained in the saga, there is an account of the origin of an English colony in the Black Sea founded by one "Siward earl of Gloucester" ("Sigurðr jarl af Glocestr"), a refugee of the Norman Conquest of England.
Euthymius Zigabenus or Zigadenus or Zygadenus (Greek: Εὐθύμιος Ζιγαβηνός or Ζιγαδηνός; died after 1118) was a 12th-century monk and commentator on the Bible.
 He was a friend of the Byzantine emperor Alexius I Comnenus, for whom he wrote a lengthy work on heresies, "Panoplia Dogmatica" or "Panoply of Doctrine" (or "Full Armour of Belief").
 This began in the apostolic era and continued down to the Bogomils, some of whom he personally examined.
 The entry on the Bogomils is our main source of information about them.
 Nothing is known about his life.
Alexios IV Angelos or Alexius IV Angelus (Greek: Αλέξιος Δ' Άγγελος ) (c. 1182 – 8 February 1204) was Byzantine Emperor from August 1203 to January 1204.
 He was the son of Emperor Isaac II Angelus and his first wife, an unknown Palaiologina, who became a nun with the name Irene.
 His paternal uncle was Emperor Alexius III Angelus.
New England (Latin: "Nova Anglia" ) was a colony allegedly founded in the late 11th century by English refugees fleeing William the Conqueror.
 Its existence is only attested in two sources, dating from the 13th and 14th centuries, the French "Chronicon Universale Anonymi Laudunensis" and the Icelandic "Játvarðar Saga".
 They tell the story of a journey from England through the Mediterranean Sea that led to Constantinople, where the English refugees fought off a siege by heathens and were rewarded by the Byzantine Emperor Alexius I Comnenus.
 A group of them were given land to the north-east of the Black Sea, reconquering it and renaming their territory "New England".
 Though these sources are late, New England is thought by some historians to be based on a reality.
Alexios Komnenos, latinised as Alexius Comnenus (Greek: ), was the eldest son of the Byzantine emperor John II Komnenos and his wife Eirene of Hungary.
 He was born in February 1106 at Balabista in Macedonia, was made co-emperor with his father at 16 or 17 years of age and died on 2 August 1142 at Attalia, Pamphylia.
 He was an elder brother of the emperor Manuel I Komnenos, and had a twin sister, Maria Komnene (plus other siblings).
Basil the Physician (died 1118) was the Bogomil leader condemned as a heretic by Patriarch Nicholas III of Constantinople and burned at the stake by Byzantine Emperor Alexius I Comnenus.
Theodora Angelina was the only daughter of Anna Angelina and the "sebastocrator" Isaac Comnenus.
 Her maternal grandparents were Byzantine emperor Alexius III Angelus and Euphrosyne Doukaina Kamaterina.
Alexios II Komnenos or Alexius II Comnenus (Greek: Αλέξιος Β’ Κομνηνός, "Alexios II Komnēnos" ) (10 September 1169October 1183) was Byzantine emperor from 1180 to 1183.
 He was the son of Emperor Manuel I Komnenos and Maria, daughter of Raymond of Poitiers, prince of Antioch.
 He was the long-awaited male heir and was named Alexius as a fulfilment of the AIMA prophecy.
Perama (Greek: Πέραμα ) is a town and a former municipality in the Ioannina regional unit, Epirus, Greece.
 Since the 2011 local government reform it is part of the municipality Ioannina, of which it is a municipal unit.
 It lies about 4 km north of central Ioannina.
 The town's name means "passage" and it lies on the northern edge of lake Pamvotis (Greek Παμβώτις).
 It is famous for its cave, known as the "Cave of Perama" (Greek Σπήλαιον Περάματος).
 The cave, extending five kilometres below the ground and having been explored fully only up to one kilometre, has a remarkable arrangement of stalagmites and stalactites.
 An 11th-century church in the town dedicated to Saint Haralambos and reputedly built by Byzantine Emperor Alexius Comnenus is in a bad state of repair and is rarely open to the general public.
 The town lies on GR-6 between Igoumenitsa and Metsovo.
Alexios I Megas Komnenos or Alexius I Megas Comnenus (Greek: Αλέξιος Α΄ Μέγας Κομνηνός, "Alexios I Megas Komnēnos" ; c. 1182 – 1 February 1222) was, with his brother David, the founder of the Empire of Trebizond, which he ruled from 1204 until his death in 1222.
 The two brothers were the only male descendants of the Byzantine Emperor Andronikos I, who had been dethroned and killed in 1185, and thus claimed to represent the legitimate government of the Empire following the conquest of Constantinople by the Fourth Crusade in 1204.
 Although his rivals governing the Nicaean Empire succeeded in becoming the de facto successors, and rendered his dynastic claims to the imperial throne moot, Alexios' descendants continued to emphasize both their heritage and connection to the Komnenian dynasty by referring to themselves as Megas Komnenos or Grand Komnenos.