Why was the US 1000 dollar bill printed?

High-denomination bills ($500, $1000, $5000, and $10,000) were first printed because at the time there were few alternatives for conveniently dealing with large amounts of money. Checks were uncommon and of course things like electronic funds transfers were over a century in the future.

The two largest denominations saw limited use, mostly by very wealthy people such as industrialists or, later, casino owners. The other denominations were used by businesses in the days when most transactions were cash-only. For example, a company ordering a large number of supplies might pay for them using $1000 bills rather than multiple fifties or hundreds.

Demand for high-denomination bills remained low into the middle of the 20th century, especially as other, more-secure forms of payment came into wider use. The final series were dated 1934 but remained in print until 1945, at which time the Treasury suspended further production.

Unfortunately the convenience of using just a few bills to carry large amounts of money led to their use in various criminal activities. In 1969 President Nixon issued and executive order permanently ending production, and ordering banks to hold any large-value bills they received for return and destruction by the Treasury.

Large-value bills weren't demonetized and people weren't ordered to turn them in, but this "passive withdrawal" process effectively removed them from circulation within a few years. Any that remain are technically still legal to spend but they're now worth more to collectors.