This paper focuses on technical endeavors to develop bio-inspired dolphin-like robots, involving dynamic modeling, mechanical design, as well as motion control. The inspiration and motivation comes from the remarkable swimming abilities of dolphins together with some promising applications in aquatic environments. The thrust in dolphin-like movements in a robotics context can be generated by the up-down-motioned fluke, while the turning is achieved by left-right-sided deflections. Based upon three generations of link-based robotic prototypes, experiences and lessons accumulated in the course of producing these accomplishments are summarized, which provide insight into unraveling the efficient and agile propulsive mechanisms associated with Gray's paradox. Comparative results are finally offered to demonstrate significant differences between biological dolphin and actual robots.