The Champion debuted in 2602 from Bergan Industries, their second-ever BattleMech after the highly-successful Locust, as a generalist combat 'Mech with a focus on heavy reconnaissance and fast strike capabilities. While definitely faster and more maneuverable than other heavy 'Mechs, it was criticized by many for being too large, underarmed and underarmored. Indeed Earthwerks Incorporated had a competing bid, a modified version of their 55-ton Griffin, which had the same performance capabilities and cost less. In the end Bergan won the lobbying wars and an initial order of 200 Champions were produced for the Star League Defense Force.
Despite its serious flaws the Champion was one of the most popular 'Mechs with the SLDF: in a era mostly marked by small skirmishes and duels where tactical positioning was key, its swiftness was sufficient enough for many pilots. It served in many of the SLDF's independent BattleMech regiments, and when newer designs began to outpace it the 'Mech was sold to the Star League's member states. Unfortunately Bergen's New Earthfactory was destroyed in 2776 during the Amaris Civil War, and in the Succession Wars that followed the Champion suffered heavy losses. Eventually the loss of the advanced technology which went into making the Champion forced many surviving 'Mechs to be refitted with lesser components. Towards the end of the Succession Wars a few Champions could still be found in the arsenals of the Great Houses, with the Capellan Confederation just barely fielding the most followed by the Lyran Commonwealth.
ComStar was able to maintain a number of original Champions in their secret stockpiles which were later used to outfit the Com Guards and the Clans maintained the aging design for their garrison forces, which they brought along during the Clan Invasion. A number of ComStar Champions were upgraded prior to the pivotal Battle of Tukayyid, among several designs which informally were known as Clanbusters, and eventually production of original-model Champions was restarted at Bergen's New Earth facility in the late 3050s. A new variant was eventually produced for ComStar and after the ComStar Schism the Champion could be found in the hands of the Word of Blake. [Source: sarna]
You can download the papercraft model here: MechWarrior 3 - Champion Free BattleMech Paper Model Download