Various theories have been proposed about the origins and development of the valkyries from Germanic paganism to later Norse mythology. Rudolf Simek suggests valkyries were probably originally viewed as "demons of the dead to whom warriors slain on the battlefield belonged", and that a shift in interpretation of the valkyries may have occurred "when the concept of Valhalla changed from a battlefield to a warrior's paradise". Simek says that this original concept was "superseded by the shield girls—Irish female warriors who lived on like the "einherjar" in Valhall." Simek says that the valkyries were closely associated with Odin, and that this connection existed in an earlier role as "demons of death". Simek states that due to the shift of concept, the valkyries became popular figures in heroic poetry, and during this transition were stripped of their "demonic characteristics and became more human, and therefore become capable of falling in love with mortals [...]." Simek says that the majority of the names of the valkyries point to a warlike function, that most of valkyrie names do not appear to be very old, and that the names "mostly come from poetic creativity rather than from real folk-belief."