Here is how he is described in Grove's Dictionary of Music (1879 ed.):
GUSIKOW, Michael Joseph, an artist of rare musical faculty —' a true genius,' says Mendelssohn—born of poor Jewish parents and of a family which had produced musicians for more than a century, at Sklow in Poland, Sept. 2,1806. He first played the flute and tympanon, a kind of dulcimer. At the age of seventeen he married, and a few years after discovered that weakness of the chest would not allow him to continue playing the flute. He thereupon took up the Strohfiedel, an instrument of the dulcimer kind, composed of strips of fir on a framework of straws, which he improved and increased in compass. (See Xylophone.) Upon this he attained extraordinary facility and power. In 1832 he and four of his relatives began a long tour, through Odessa—where he was heard by Lamartine; Kiev—whore he was much encouraged by Lipinski; Moscow; and thence to south and north Germany, Paris, and Brussels. He travelled in the dress and guise of a Polish Jew—long beard, thin, pale, sad, expressive features—and excited the greatest applause by his astonishing execution and tho expression which he threw into his unlikely instrument. Mendelssohn heard him at Leipzig, and called him 'a real phenomenon, a killing fellow (Mordkerl); who is inferior to no player on earth in style and execution, and delights me more on his odd instrument than many do on their pianos, just because it is so thankless. . . . I have not enjoyed a concert so much for a long time' (and see the rest—Letter, Feb. 18, 1836). But it wore him out; he was laid up at Brussels for long, and died at Aix la Chapelle, Oct. 21, 1837, adding another to the list of geniuses who have died shortly after thirty. (See Fetis, who saw much of him.)I guess that's mid-19th century German slang; he was a Mordkerl ("a killing fellow"). Do people still say "killer musician"? I guess "shortly after 30" was the 27 of the 19th-century. His instrument, the Strohfiedel ('straw fiddle') was basically a kind of xylophone. He allegedly invented it, but the truth about that appears to be more complex.
Here is what he and his instrument looked like:
And if you prefer to see him in his Litvishe yarmulke:
Here is a letter Felix Mendelssohn-Bartholdy sent to his mother in 1836:
You can listen to what is described as his "single surviving composition," for Shir Hamaalos: