Important building blocks of software engineering concepts are without a doubt technical. During the last decade, research and practical interest for non-technicalities has grown, revealing the building blocks to be various skills and abilities beside pure technical knowledge. Multiple attempts to categorise these blocks have been made, but so far little international studies have been performed that identify skills by asking experts from both the industrial and academic world: which abilities are needed for a developer to excel in the software engineering industry? To answer this question, we performed a Delphi study, inviting 36 experts from 11 different countries world-wide, affiliated with 21 internationally renowned institutions. This study presents the 55 identified and ranked skills as classified in four major areas: communicative skills (empathy, actively listening, etc.), collaborative skills (sharing responsibility, learning from each other, etc.), problem solving skills (verifying assumptions, solution-oriented thinking, etc.), and personal skills (curiosity, being open to ideas, etc.), of which a comparison has been made between opinions of technical experts, business experts, and academics. We hope this work inspires educators and practitioners to adjust their training programs, mitigating the gap between the industry and the academic world.