Tri-series is a series/tournament with three nations playing for the trophy.
When was the first international tri-series for cricket matches held?
Which nations participated in it and who was the winner?
The first tri-series Test tournament was held in England in 1912, between England, Australia, and South Africa, and was won by England.
The first tri-series ODI tournament was held in Australia in 1979, between Australia, West Indies, and England, and was won by West Indies.
There appears to have only been one T20 tri-series (all the other tournaments in the list had more than three teams) so far, held in 2010 between Kenya, Uganda, and Scotland, and the hosts Kenya were the victors.