Kobzar is a folk singer who singing and accompany himself with kobza (string instrument played by plucking). This singing is common in Ukraine in past and now, and its performers rightly called kobzars (with lowercase).
However, in Ukraine living word Kobzar (capitalized). This word means Taras Shevchenko, only him and nobody more (the Muslims have a special word – tahallus – pseudonym of the poet, which replaces his own name…)
The first book of poems by Shevchenko was published in 1840 entitled "Kobzar". It contained only 8 pieces. After return from exile, Shevchenko in 1858 tried to publish his collection of poetry entitled "Poetry of Taras Shevchenko. The First Volume", but the tsarist censorship categorically denied it. At the same time the name "Kobzar", as already admitted by censors before, did not cause any objections. As a result this new, greatly expanded collection of poems was published in 1860, also called "Kobzar". It was the lifetime summary edition of Shevchenko's poetry and created a publishing tradition – combine all Shevchenko's poetic heritage as "Kobzar".
We also follow this tradition and call the chronologically ordered collection of poetry – "Kobzar".