Thanks David for changing my username from Arhat to Bharadwaja.
OK let's start with Māra. This is not a proper name, it is an epithet, meaning "death" (from the verbal stem "mar-" i.e. to die). Keep in mind death was not viewed as an absolute in Indian culture, it is as temporary (and fleeting) as life. Māra (as the personification of death) is called so, since he causes spiritual death, and his quest is to keep the individual mired in saṃsāra (i.e. submerged within the "stream" of the life-death-life-death... swirl), whilst the Buddha by defeating him and keeping him in check has managed to cross the "stream" and figuratively "reach the other shore" and has thus escaped the duality of becoming/birth and unbecoming/death, hence he gets the epithet tathāgata (the one thus gone forth, to the other shore). The buddha takes the help of the raft called "dhamma" (i.e. dharma, dhar = "to bear") to cross the stream of saṃsāra and to that extent the vijjā "knowledge" of dhamma is the guide (acting against the "avijjā", which nivuta "covers/envelopes" the world) that takes one from the duality of saṃsāra, to the non-duality of nibbāṇa. Taṇhā (sensual thirst or craving), Arati (disgust), and Raga (inflammation/deep-passion) are figuratively the daughters of Māra who help him, to keep the individual mired in saṃsāra and not letting him/her reach the other shore. Hence the Buddha's battle with Māra and his conquest of Māra is an important occasion for it signifies the ascent to Buddha-hood (or arahant-hood). Māra does not go away, he keeps coming back to the Buddha with his daughters to tempt the buddha back into saṃsāra, but the buddha by striving (sramaṇa "striver" = one who undertakes srama "effort") manages to always keep Māra in check, and for this feat, he is called an arahant (i.e. ari "enemy"+ hant "destroyer").