Who designed Lithuania's flag?

Answer 1

In ancient times, it was customary to have state, not national flags. Lithuania did not have a national flag also. The state flag of the Great Duchy of Lithuania was red with a white Vytis (an armored knight riding a white stallion leaping forward, with the knight holding a raised sword high over his head). This flag was used throughout Lithuanian history.
During the era of national rebirth (end of 19th and beginning of 20th centuries) Lithuanians fought for and sought freedom for their country. But many did not believe in a free tomorrow. They would have been satisfied if the Russian czar had agreed to give Lithuania more rights or self-government without breaking all ties with Russia. Such a solution seemed more attainable.
After the 1905 revolution, and especially during World War I, Lithuania's hopes of re-establishing an independent state grew vigorously. It appeared that the Russian empire was not so invincible nor the czar's government so omnipotent. The hypothesis of independence was not only possible but completely feasible. It was at this time that the question of a national flag for independent Lithuania arose.
The question was especially widely debated in 1917 at the Conference of Vilnius. In the end, the Council of Lithuania was given the task of resolving the matter. It was suggested that one of the old flags of the Duchy of Lithuania with their familiar Vytis and Columns of Gediminas symbols be adopted. Several new proposals for flags were also drafted. A flag commission composed of Dr. Jonas Basanavicius, artist Antanas Zmuidzinavicius and Tadas Daugirdas submitted a proposal which the Council of Lithuania adopted on April 19, 1918. The newly-adopted Lithuanian flag was composed of three equal horizontal stripes of yellow, green, and red. According to Dr. Basanavicius, the colors were selected because they recur most often in Lithuanian folk weavings arid other folk art. Today, they are explained as follows:
yellow. the fertile fields of Lithuania, golden with ripe rye, wheat, flax, and other grains;
green : the symbol of the nation's vitality (as represented in nature also);
red : the blood shed in defending the homeland's freedom.
The adopted Lithuanian flag was also included in the Lithuanian Constitution. The tricolor was publicly raised for the first time on November 11, 1918 in Vilnius, at the Council of State building. It was widely used during Lithuania's independence until the first Bolshevik occupation in June 1940.
After the long 48 years break, from 7 October of 1988, the tri-color flag of pre-war, independent Lithuania is raised on Gediminas Castle.

Answer 2

If I am not mistaking (and I might be), it was agreed upon by the Lithuanian parliament in the early 1920s. But you better check the wikipedia.

Answer 3

Very good information source is http://www.crwflags.com/fotw/flags/lt.html