Legally (canonically) elected Anti-Pope of the Roman Catholic Church

Anti-pope in a practical sense means, two elected Pope at the same time and both mutually declared each other as the candidate of Satan Lucifer. They excommunicated each other, they tried to kill each other. It is not possible to establish the numbers of Ant-pope due to the destruction of documents and deletion from the church history, even then there were at least 40  popes from 217 to 1439. For example, Hippolytus opposed to Pope Callixtus I (217–222). Felix V, was Pope until 1449, then he stepped down and became a Cardinal, now considered the last anti-pope.

We listed 29 of them as below:

1. Hippolytus, III century
2. Novatian, 251
3. Felix II, 355-365
4. Ursicinus, 366-367
5. Eulalius, 418-419
6. Laurentius, 498-501
7. Constantine II, 767
8. Philip, VIII century
9. Anastasius, 855
10. Leo VIII, 956-963
11. Boniface VII, 974
12. John XVI, X century
13. Gregory, 1012
14. Sylvester III, 1044
15. Benedict X, 1058
16. Honorius II, 1061-72
17. Guibert or Clement III, 1080-1100
18. Theodoric, 1100
19. Aleric, 1102
20. Maginulf, 1105
21. Burdin (Gregory VIII), 1118
22. Anacletus II, 1130-38
23. Victor IV, 1159-64
24. Pascal III, 1164-68
25. Calixtus III, 1168-77
26. Innocent III, 1178-80
27. Nicholas V, 1328-30
28. Robert of Geneva (Clement VII), 20 September, 1378 to 16 September, 1394
29. Amadeus of Savoy (Felix V), November, 1439 to April, 1449