WILMINGTON, Del. (AP) — Jill Biden is a prankster. The wife of presumptive Democratic presidential nominee Joe Biden once sneaked into a close aide’s birthday party dressed as catering staff and surprised him with a drink. She has dressed up as the Grinch to toy with colleagues during Christmas. Friends say Jill Biden’s sense of humor has helped her husband navigate decades in public life that have been marked by achievements, defeats and considerable personal loss. As she prepares to speak Tuesday at the Democratic National Convention, those who have worked closely with Jill Biden say her warmth will appeal to Americans confronting tough times of their own.