Giridhar is the name of one of Gods in Hindu religion. So which God is known as Giridhar? Giri means mountain. Giridhar is one who lifted the mountain. Yes, Giridhar is Lord Krishna.
Krishna got the name Giridhar after lifting the mountain Govardhan.
The story of Krishna lifting Govardhan Mountain is found in the Harivamsha, Srimad Bhagavad Purana and numerous other scriptures.