Final answer:
Transformational Leadership Theory is the most widely accepted theory by Bernard Bass, emphasizing the effectiveness of leaders with charismatic, inspirational, intellectually stimulating, and considerate characteristics.
Step-by-step explanation:
The theory defining how people become leaders according to Bernard Bass that is most widely accepted is Transformational Leadership Theory. This theory is extensively endorsed within the field of Industrial-Organizational (I-O) research and suggests that leaders possess four distinct attributes: they are charismatic, inspirational, intellectually stimulating, and considerate. Research carried out by Eagly, Johannesen-Schmidt, & van Engen in 2003 highlights that transformational leadership is empirically found to be more effective than transactional leadership styles, indicating a broad consensus for its effectiveness.