The Data Encryption Standard was based on the work of Horst Feistel. DES became the standard in 1976 (published in 1977) when it was selected by National Bureau of Standards (NBS) of the United States. DES was a modified version of Lucifer algorithm developed by Feistel. Lucifer had key size of 128 bit, when the DES was published the key size was reduced to 56 bit. DES has block size of 64 bit which means it can encrypt 64 bits in it's one cycle of operation.
Triple DES (3DES):
Triple DES was based on DES algorithm. When DES was cracked, the use of 3 cycles of DES was proposed as a secure alternate without having the need to develop a new more stronger algorithm from scratch. As the DES had key size of 56 bit, the 3 cycles of DES with 3 different keys made the key size of 168 bit. However 112 bit and 56 bit variants were also identified but are generally not used as they do not provide effective security. Triple DES is not a standard. The new standard is known as Advance Encryption Standard (AES) which is based on Rijndael algorithm.