"Decrepit elder, senior" could be
THEODEN - the clue has 'Mark' in it, and 'not senile, nor yet weak' could refer to his recovery after
not being hit around the head by Gandalf.
'to describe a whacker' immediately makes me think
BEATER, AKA Glamdring.
Loving the Elbow of Sauron in the second clue.
hS