Why do the Shiites hate ‘Umar ibn Al-Khattaab, may Allaah be pleased with him?

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

The Prophet told ‘Umar, may  Allaah be pleased with him, that whenever Satan sees him walking along a particular road, Satan runs away from it and takes another one because he fears him and the strength of his faith. [Al-Bukhari and Muslim] 

In another Hadeeth (narration) on the authority of Abu Moosaa Al-'Ash‘ari, when the Prophet sat by the door to the well of 'Arees and ‘Umar ibn Al-Khattaab asked permission to enter, he ordered Abu Moosaa to give him permission to enter. He also brought him glad tidings that he will enter Paradise. [Al-Bukhari and Muslim]

Therefore, because ‘Umar was held in such high esteem by the Prophet anyone who hates him or shows enmity towards him will be considered to be at war with Allaah The Almighty and His Messenger. This is because he has adopted a way other than that of the believers. This is especially so since Allaah The Almighty made Islam dominant at his hands and many nations embraced Islam through him. Allaah The Almighty Says (what means): {And whoever opposes the Messenger after guidance has become clear to him and follows other than the way of the believers -- We will give him what he has taken and drive him into Hell, and evil it is as a destination.} [Quran 4:115]

Nevertheless, some Shiite sects hate ‘Umar ibn Al-Khattaab and they even consider the Companions to be disbelievers except a few; no more than seven or nine. They harbor a special grudge against ‘Umar out of spite and loathing for this rightly-guided Companion, because he was the person who extinguished the fire of the Magians and caused the decline of their kingdom.

Some of them even venerate Abu Lu'lu'ah Al-Majoosi, the man who murdered ‘Umar .

Allaah Knows best.