Half-brother in the context of "Sigebert I"

Castor and Pollux (or Polydeuces) are twin half-brothers in Greek and Roman mythology, known together as the Dioscuri or Dioskouroi.

Their mother was Leda, but they had different fathers; Castor was the mortal son of Tyndareus, the king of Sparta, while Pollux was the divine son of Zeus, who seduced Leda in the guise of a swan. The pair are thus an example of heteropaternal superfecundation. Though accounts of their birth are varied, they are sometimes said to have been born from an egg, along with their twin sisters Helen of Troy and Clytemnestra.

Deva (Sanskrit: देव, Sanskrit pronunciation: [de:vɐ]) means 'shiny', 'exalted', 'heavenly being', 'divine being', 'anything of excellence', and is also one of the Sanskrit terms used to indicate a deity in Hinduism. Deva is a masculine term; the feminine equivalent is Devi. The word is a cognate with Latin deus ('god') and Greek Zeus.

In the earliest Vedic literature, all supernatural beings are called Devas and Asuras. The concepts and legends evolved in ancient Indian literature, and by the late Vedic period, benevolent supernatural beings are referred to as Deva-Asuras. In post-Vedic Hindu texts, such as the Puranas and the Itihasas of Hinduism, the Devas represent the good, and the Asuras the bad. In some medieval works of Indian literature, Devas are also referred to as Suras and contrasted with their equally powerful but malevolent half-brothers, referred to as the Asuras.

Agravain or Agravaine (/ˈæɡrəveɪn/ AG-rə-vain) is a Knight of the Round Table in Arthurian legend, whose first known appearance is in the works of Chrétien de Troyes. He is the second eldest son of King Lot of Orkney with one of King Arthur's sisters known as Anna or Morgause, thus nephew of King Arthur, and brother to Sir Gawain, Gaheris, and Gareth, as well as half-brother to Mordred.

Agravain secretly makes attempts on the life of his hated brother Gaheris starting in the Vulgate Cycle, participates in the slayings of Lamorak and Palamedes in the Post-Vulgate Cycle, and murders Dinadan in the Prose Tristan. In the French prose cycle tradition included in Thomas Malory's Le Morte d'Arthur, together with Mordred, he then plays a leading role by exposing his aunt Guinevere's affair with Lancelot, which leads to his death at Lancelot's hand.