Rural aging and labor shortages have become major constraints for primary watermelon production in Korea. In addition, the cultivation of large watermelons weighing 6-9 kg in a crouched posture imposes a heavy labor burden on farmers, leading to a continuous decline in the watermelon cultivation area. From a consumption perspective, the increasing number of small household consumers has shifted market demand from large to small to medium-sized fruits, highlighting the need for suitable cultivars. A new small to medium-sized watermelon cultivar, ‘Goldking,’ was developed to address these issues. This cultivar is suitable for vertical cultivation, enabling standing work, thereby reducing labor intensity, and producing fruits appropriate for single-household consumption and single-meal use; it is a diploid watermelon with a black rind, yellow flesh, and an oval fruit shape. The fruit weight was 6.3 kg under creeping cultivation, whereas it decreased to 4.0 kg under vertical cultivation with a planting distance of 25 cm, indicating small to medium-sized fruit. Yield under creeping cultivation was 4,892 kg/10 a, which was lower than that of ‘Sambokggul’; however, under vertical cultivation with four rows, yield increased to 9,481 kg/10 a, representing a 53.4% improvement compared to conventional creeping cultivation of large-fruited cultivars. As a result of these traits, ‘Goldking’ was applied for plant variety protection in 2022 and was officially registered as a variety (grant number No. 10317) with the Korea Seed & Variety Service in 2024.