Was the founder of Sikhism a Muslim?

Can some Sikhs tell me who founded their religion please?

No. The founder was Guru Nanak, born a Hindu.

http://en.wikipedia.org/wiki/Guru_Nanak_Dev

NO HE WAS NOT MUSLIM. He was born Hindu like the guy above me said.

No He was not a Muslim

Nanak, the founder of Sikhism, was born a Hindu and belonged to the Punjab where he lived between 1469-1539. Since Punjab was home to both Hindus and Muslims, Nanak grew up observing the ill-will between the two religious communities.

No he was a Hindu but Sikhs are descended from Hindus and Muslims who converted to Sikhism - mostly Hindus converted though.

No, he was converted to Islam but later proclaimed that he received direct revelations from god.

Dear Asker ,
Founder of Sikh religion is Guru Nanak Dev . He is also the first Guru ( spiritual teacher ) of the Sikhs .
He was born in the year 1469 AD to a Hindu Khatri family in Punjab , which is a part of Pakistan today .
He was born in a Hindu family , but was never a Hindu . He was a saint of God and a preacher of peace and love .
At the age of 9 , when he was being initiated into Hinduism ceremony . In this ceremony , Hindus put thread around a child's neck . They consider it to be holy . Guru Nanak question the significance of thread and said the true holy thread is Lord's name alone .
In this way , he rejected many useless Hindu as well as Muslim rituals .
He was neither a Hindu nor a Muslim and preach that we are all humans and same in eyes of God .
He was just a messenger of peace .

"There is no Hindu , no Muslim " is his famous saying.

Guru Nanak rejects Hindu rituals
http://www.sikhiwiki.org/index.php/The_Hindu_Sacred_Thread,_Janeu

You should have go ogled it, there is a lot of material on guru Nanak or Sikhism. reading about Guru Nanak will not pollute you.