Why Guru Gobind Singh Jayanti is celebrated? 

One of  his notable contributions is said to be in 1699 when he founded the Sikh  warrior community called the Khalsa. Guru Gobind Singh Jayanti is being  celebrated on Thursday, December 29, to mark the 355th birth anniversary as per the lunar calendar of Guru Gobind Singh, the tenth Guru of the Sikh community 

Which Sikh Guru was killed by Mughals? 

Two Sikh leaders, Guru Arjan and Guru Tegh Bahadur,  were executed by order of the reigning Mughal emperor on grounds of  political opposition. The 10th and last Guru, Gobind Singh, before his  death (1708) declared the end of the succession of personal Gurus.