there is sigi qutuqtu , a tartar , his foster brother and his chief justice ; tartar tonga , not a tartar but a uighur , who adapted the uighur script for mongol and taught chinggis children to write ; or chingqai , a hirai turk , an old comrade of chinggis and a major government figure until 1251 , when he was a victim of the grandchildrens first internal war .