1. Canis lupus, a.k.a gray wolf. The term "timber wolf", as I see it, is used of subspecies of gray wolves that primarily live in forests. (Correct me if I'm wrong...)
2. The 'Mech favored by Clan Wolf (also the favorite of me for obvious reasons =). Maximum weight 75 tons, height 15 meters.
The Inner Sphere designation "Mad Cat" is because its distinct "hunchback" form is similiar to Marauder and Catapult 'Mechs.
The Mad Cat was the first OmniMech to appear in the Inner Sphere. Though bearing a superficial resemblance to the Inner Sphere Catapult, its advanced technology and superior weapons put an end to any comparisions. Capable of laying down a punishing barrage of weapons fire at any range, the Mad Cat has become all but synonymous with the Clans and their assault against the Inner Sphere. - found in MechWarrior 3 and MechCommander manuals, by MicroProse
Timber Wolf in its primary configuration (Timber Wolf Prime) is armed with two LRM racks (box-mounted on shoulders), bunch of lasers and machine guns. The LRM rack is Prime's coolest armament, and as such it's not really suited for combat close by - deal death from far away!
The alternate configurations are similar: A carries PPCs, B carries a gauss rifle and Artemis IV FCS, C carries lasers and an Ultra AC/5, and D has PPCs - with two double Streak SRM-6 racks that point to both forward and backwards.
See also: BattleTech, David L. Mech =)