HiFi

HiFi was the stuffed panda mascot of Steven Taylor, who grew very fond of him during his two years of isolation on Mechanus. During the fire in the Mechanoid City, Steven risked his own life in order to rescue him. (DW: The Chase) Steven took HiFi with him into the TARDIS. (DW: The Time Meddler)  He was never seen after Steven's initial voyage in the TARDIS, haven been given as a gift to Bobby Zierath (ST: The Schoolboy's Story).
 * ''The name seems to be a reference to a term popular in English of the 1960s and 60s for a high quality stereo system. However, it may have a dual meaning.  Since "HiFi" is a contraction of the term "High Fidelity", it may also be a reference to the loyalty Steven displayed towards the object in rescuing it from the burning Mechanus, or the fact that the stuffed animal was Steven's one constant companion during his captivity.