Shape adaptable hydrogel actuators, capable for changing their shapes in response to single or multiple thermo/other external stimulus, are considered as new emerging smart materials for a broad range of fundamental/industrial research and applications. This review mainly focuses on the recent progress (particularly over the past 5 years) on such thermo-responsive hydrogel actuators. Recent fundamental advances and engineering applications in materials design/synthesis/characterization, distinct actuation mechanisms, and intriguing examples of these hydrogel actuators of single or dual stimuli are selectively presented. Specific or general design principles for thermo-induced hydrogel actuators are also provided to better illustrate the structure-property relationship. In the end, we offer some personal perspectives on current major challenges and future research directions in this promising field. Overall, this review discusses current status, progress, and challenges of hydrogel actuators, and hopefully will motivate researchers from different fields to explore all the potentials of hydrogel actuators.