tumbler doll; self-righting doll
A traditional roly-poly toy that rights itself when pushed over. This term is literary and uncommon in everyday speech; the more familiar word is 起き上がり小法師 (おきあがりこぼし) or simply だるま.
See also: 起き上がり小法師 (おきあがりこぼし)
A 不倒翁 is a lucky toy that rights itself immediately when knocked over.
From Chinese 不倒翁 (bùdǎowēng), literally 'old man who does not fall'. The Japanese reading is on'yomi.