How much control do the characters in Beowulf have over their fates? Are skilled warriors any more likely to succeed than cowards? Who does the narrator remind us is calling all the shots?

In Beowulf the fate of the characters are ultimately decided by God. Although if a character is strong and brave, he would be favored more by fate instead of a weak and cowardly character. Overall, the characters in Beowulf can only improve themselves in order to gain favor with fate, but in the end, (as the narrator often reminds us) God, is the ultimate deciding factor.

The characters in Beowulf only have control of themselves in terms of how much strength and courage they have as they enter the battle. If they were to have great strength and courage, they would be favored by fate more. If they were to be weak and cowardly, fate would not be in their favor. Beowulf explains to Hrothgar about fate and God in relation to his upcoming fight against Grendel:

“Whichever one death fells

must deem it a just judgement by God.

If Grendel wins, it will be a gruesome day;

. . .

No need then

to lament for long or lay out my body

. . .  

Fate goes ever as fate must” (440-455).

According to Beowulf, God chooses who will be the one to live or die. If he was too weak to defeat Grendel, then Hrothgar should not bother having a funeral for him since it is his fate to die because he was not strong enough to defeat Grendel. In other words, fate is determined by the strength of the character, but the ultimate result is determined by God.
The narrator of Beowulf often reminds the reader that God is the one who is calling the shots. The narrator says, “So may a man not marked by fate / easily escape exile and woe / by the grace of God” (2291-2293) when he tells the readers about the dragon’s fury. Meaning, hopefully all the innocent people, who did not disturb the dragon, be spared by God. Another example of the narrator reminding the readers that God is the one calling the shots is: “The truth is clear: / Almighty God rules over mankind / and always has” (700-703).