Modi and Magni

In Norse mythology, Móði (anglicized Módi or Mothi) and Magni are the sons of the thunder-god, Thor. Their names translate to "Courage" and "Mighty," respectively. Rudolf Simek states that, along with Thor's daughter Þrúðr ("Strength"), they embody their father's features.

Móði and Magni's descent from Thor is attested by the kennings "Móði's father" (faðir Móða, in Hymiskviða, 34) and "Magni's father" (faðir Magna, in Þórsdrápa and Hárbarðsljóð, 53). Snorri Sturluson confirms it (Gylfaginning, 53, Skáldskaparmál, 4). According to Skáldskaparmál (17) Magni is the son of Thor and the Jǫtunn Járnsaxa. There is no mention of Móði's mother.

Poetic Edda
The two brothers are mentioned among the survivors of Ragnarök in the Poetic Edda Vafþrúðnismál:

Prose Edda
Apart from his role after Ragnarök, there is nothing we know about Móði but, in the Prose Edda book Skáldskaparmál, Magni plays a role in the myth of Thor's battle with the giant Hrungnir:
 * But the hammer Mjölnir struck Hrungnir in the middle of the head, and smashed his skull into small crumbs, and he fell forward upon Thor, so that his foot lay over Thor's neck. Thjálfi struck at Mökkurkálfi, and he fell with little glory. Thereupon Thjálfi went over to Thor and would have lifted Hrungnir's foot off him, but could not find sufficient strength. Straightway all the Æsir came up, when they, learned that Thor was fallen, and would have lifted the foot from off him, and could do nothing. Then Magni came up, son of Thor and Járnsaxa: he was then three nights old; he cast the foot of Hrungnir off Thor, and spake: 'See how ill it is, father, that I came so late: I had struck this giant dead with my fist, methinks, if I had met with him.' Thor arose and welcomed his son, saying that he should surely become great; 'And I will give thee, he said, the horse Gold-Mane, which Hrungnir possessed.' Then Óðinn spake and said that Thor did wrong to give the good horse to the son of a giantess, and not to his father.
 * —Skáldskaparmál (17), Brodeur's translation

John Lindow draws a parallel between Magni and Odin's son Váli for they both have a giantess mother (Rindr for Váli) and achieve a feat at a very young age (Váli is only one day old when he kills Höðr, thus avenging Baldr's death).

Family
Móði and Magni are the sons of Thor, and the brothers to Þrúðr.