Clue: Refuse working with international telecom pioneer (7)
Answer: MARCONI
Explanation: Definition: telecom pioneer
 MARC(the refuse from grapes that have been pressed in wine-making) + ON(working/operating, such as an electrical appliance) **plus**(with) I(abbrev. for "international").
Answer: …, Guglielmo, Italian inventor of a practical radiotelegraphy system, a pioneering telecommunications technology.