This thesis reports the early-stage development of the Terahertz Intensity Mapper (TIM). TIM isa balloon-borne far infrared (FIR) telescope fielding novel cryogenic kinetic inductance detectors. TIM combines two long-slit grating spectrometers to cover 240-420 microns at a resolving power of R = 250. Building on the flight heritage of the BLAST and SPIDER balloon programs, TIM will wield sub-arcsecond pointing reconstruction to create a 4-D tomographic map of the redshifted [CII] emission line over the GOODS-South/Chandra deep field at ∼ 0.2 square degrees across a redshift range 0.5 ≲ z ≲ 1.7. This will allow TIM to apply (and demonstrate) the novel line intensity mapping (LIM) technique across roughly 5 billion years of cosmic history, which spans the plateau and subsequent decline of cosmic star-formation. This thesis will focus on three sub-projects. First, the status and development of the overall TIM platform, with an emphasis on the design and implementation of the new modular, open-source power distribution system. Second, the testing and characterization of TIM’s final prototype KID array. Finally, a forecast of TIM’s key scientific project, a [CII] cross power intensity map with the galaxy density field as observed by the Euclid space telescope in their deep field Fornax.