Final answer:
The correct answer is option a. His involvement in organized crime and criminal activities.
Step-by-step explanation:
The reputation of Al Capone, a notorious gangster of the Prohibition era, was ultimately ruined by his involvement in organized crime and criminal activities, including bootlegging, prostitution, gambling, loan sharking, and murder.
Despite his philanthropic efforts and contributions to charitable groups, the violent nature of his criminal empire and the numerous gang-related killings associated with him damaged his public image.
His downfall came when the FBI shifted their focus to his business's financial indiscretions, leading to his conviction for tax evasion.