Mac, or MAC08 (Mechanical Assistance Computer 08) is an outdated model of the MAC series, which is a series of robots designed to work in factories, usually specifically the ones that build robots. 

The line of MAC he is from do not have some facial features, such as a mouth, which the human workers found unsettling. They also cannot speak beside a few prerecorded messages, which was also considered  unsettling.

He thinks in binary code and can connect to the internet but only via a dial-up connection. This line of robot can also be connected to computers via USB.

Mac was thrown out years ago due to him getting a virus which unlocked a sort of autonomy in him, which led to his entire line of bot being scrapped and remade (the currently line is MAC10). He was left in a scrapyard, switched off until Izzy came across him and switched him back on again. He is supposedly the only remaining MAC08 in one piece, since they were all thrown out. Support for his line of robot is no longer available from the manufacturer. Izzy drew the smile on the surgical mask on his face. They stick together after meeting.

Mac thinks that Cassandra is a weird and terrible invention. Nothing against her just... wow. What an insane use of this tech...