Mirza Ghulam Ahmad Qadiani is a founder of a religous cult called "Ahmadiyya Jammat/Qadianism/Ahmadiyyah" his followers are also referred to as Qadianis & Ahmadis. The Qadianis claim that Mirza Gulham Ahmad Qadiani was a Prophet of God and a Promised Messiah, as well as a host of other things. Sadly his followers claim to follow Islam & that they are part of the Muslim Community (Ummah). When in reality their beliefs sadly takes them out of the fold of Islam.
It is the fundamental belief of 1.5 billion Muslim population worldwide, that there is NO Prophet after Prophet Muhammad صلى الله عليه وسلم. The Prophets عليه السلام were specially selected by Allah to convey His message to mankind & were not self selected. This door of Prophethood was closed when the final messenger of God appeared in Arabia i.e. Prophet Muhammad صلى الله عليه وسلم .
When one wishes to search the fundamental beliefs of any religion, denomination or cult, then one must first of all strengthen one's knowledge of its founder, its principles and its message.
The founder of the Ahmadiyya Movement (Qadiani religion) otherwise known and documented as "Qadiani" or "Mirzai" was called Mirza Ghulam Ahmad, born in Qadian, a village in Punjab, India, in 1839 or 1840, died in Lahore 1908 and buried in Qadian. He initially claimed to be a reformer, Mahdi, then in 1891 he claimed to be Jesus, son of Mary and in 1901 he claimed to be a prophet of God. Finally he claimed to be God himself (Kitab al Bariyya, pg 85, Roohani Khazain, Vol 13, pg 103,). The Qadianis were created to deepen divisions amongst the Muslims as a whole in the Indian subcontinent (during the British Raj). Mirza Qadiani has a uniqiue characteristic, his ability to abuse and insult people throughout his life.
His hatred and abuse for Prophet Isa عليه السلام (Jesus) is well established in his own books, he writes:
"Jesus had an inclination for prostitutes perhaps due to his ancestral relationship with them, otherwise
no pious man could allow a young prostitute to touch his head with her filthy hands...." Zamimah Anjam-i-Atham, Roohani Khazain, Vol.11, P.29
In another place, Mirza claims superiority over Prophet Isa عليه السلام:
"God sent the promised Messiah (i.e. Mirza Ghulam) amongst this community who is better in all his glory than the first Messiah (i.e. Jesus)" Dafi' Al-Bala, Roohani Khazain, Vol.18, P.233
Not only did Mirza Ghulam Qadiani use such insulting language for Prophet Isa عليه السلام, he also abused and cursed any person that spoke out against him or did not believe in him to the extent that he refused to attend the funeral prayer of his own son. He referred to those who rejected him as 'the children of Prostitutes'
"All Muslims (Qadianis) regard my books with reverence and care and benefit from their sublime thoughts except those who are the offspring of prostitutes (bastards); God has put a seal upon their hearts and they do not accept me." Roohani Khazain, Vol.5, Aina-e-Kamalat Islam, P.547-548
After reading the above quote, one would ask as to what was the wife of Mirza Ghulam Qadiani?
As well as abusing the Prophets of Allah, Mirza Qadiani claimed to be the REINCARNATION of the last and final Prophet Muhammad صلى الله عليه وسلم
"In this revelation "Mohammadur Rasoolullah wal lazeena m'ahoo, ashiddao 'al alkuffare rohamao bainahum" (Muhammad is the messenger of Allah. And those with him are hard against the disbelievers and merciful among themselves [Quran 48:29]), I (Mirza Ghulam) have been named Muhammad as well as the Messenger of Allah." Roohani Khazain, Vol.18, P.207; Ek-Ghalati-Ka-Izala, P.3/4
"I have told so many times that according to the verse "Wa Akhareen Menhom" (Along with others of them...) - in the incarnate form, I am the same last of the Prophets. Twenty two years ago, God named me in Braheen-e-Ahmadiya, Muhammad and Ahmad and declared that I am the entity of the Holy Prophet(SAW)."
Roohani Khazain, Vol.18, P.212; Ek-Ghalati-Ka-Izala, P.1/8
"The Holy Prophet(SAW) had two advents. In other words, you may say that one mission was in the reincarnated form. It was
promised that the Holy prophet(SAW) would be sent to the world once again and this was fulfilled by the advent of the
Promised Messiah and the promised Mehdi (i.e. Mirza Ghulam)."
Roohani Khazain, Vol.17, P.249; Tuhfah-e-Golravia, P.94, 1st Edition, Qadian, 1902
Please keep in mind just like Muslims don't consider Christians or Jews as Muslims we also hope that Muslims view Qadianis/Ahmadis in such light, we shouldn't abuse or mock the Ahmadis rather our approach should be one to deal with them with justice and mercy and to convey to them the teachings of Islam, especially if we are learned about this topic.
Here are some useful link:
Qadianiyyah in the light of Islam