The first computer viruses were not what they are today, they were mostly made as practical jokes to play on co-workers or designed to find idle computer processes or to see how far someone could push their coding skills.

The first real computer virus in the wild was called “Brain” and it was coded by two brothers, Basit and Amjad Farooq Alvi in 1986. It gets the distinction of being the first virus as it was the first computer virus designed to attack the IBM Personal Computer and compatibles (source).

The brothers coded the virus to protect their medical heart monitoring software that was being widely distributed without their permission. So they attached the virus to the software and it would replace the boot sector with the virus.

When the program was run, the virus would display the following:

Welcome to the Dungeon © 1986 Basit & Amjads (pvt). BRAIN COMPUTER SERVICES 730 NIZAM
BLOCK ALLAMA IQBAL TOWN LAHORE-PAKISTAN PHONE: 430791,443248,280530. Beware of this VIRUS…. Contact us for vaccination…

When the brothers began to receive a large number of phone calls from people in the United Kingdom, the United States, and elsewhere, demanding that they disinfect their machines, they were stunned and tried to explain to the outraged callers that their motivation had not been malicious. Their phone lines were overloaded. The brothers, with another brother, Shahid Farooq Alvi, continued business in Pakistan, as Brain NET Internet service providers with a company called Brain Telecommunication Limited. (source)