### Clue: He composed letter after a certain amount of work (4)
### Answer: BERG 
 ### Explanation: Definition: He composed
  'B"(the letter after "a") + ERG(in physics, a single unit,certain amount of work done equal to that of a force of 1 dyne exerted for a distance of 1 cm.). 
Answer: Alban, an Austrian he who composed music, not letters.  A nice misdirecting surface.