Multi-component soft materials offer innovative solutions for traditional and emerging technologies by possessing unique combinations of tunable functionality and adaptive mechanical response. These materials often incorporate functional inclusions such as metals or ceramics in elastomers to create deformable composite structures with high thermal or electrical conductivities, magnetic material response, or stimuli-responsive shape and rigidity tuning. In recent years, these materials have become enabling for wearable electronics and soft machines which has led to the development of new material architectures that provide advanced functionalities while maintaining a low mechanical modulus and high extensibility. In this work, we develop methods for the fabrication and utilization of advanced material architectures which integrate room temperature liquid metals (LM), low melting point alloys (LMPA), and magnetic powders and fluids with soft elastomers to introduce multifunctionality to electronic and machine systems. LM-elastomer composites which have high thermal and electrical conductivities are enabling for heat transfer applications and soft, extensible wiring for wearable electronics and soft robots. These materials have been utilized to create emerging devices such as electronics that are capable of improving human health and efficiency, as well as robots capable of adapting their functions based on environmental need. One possible area where LM composites could be applied is in marine environments, where wearable electronics can improve safety for divers, and soft machines could be utilized for underwater exploration. In Chapter 2, we provide the first study to quantify the effects of underwater aging in freshwater and saltwater environments on the important mechanical and functional properties of LM composites for long-term underwater use. It is found that LM composites are largely resistant to changes in their mechanical properties, as well as both thermal and electrical functionality due to long-term underwater aging. In Chapter 3, we introduce a new chemical approach for the tough bonding of LM composites to diverse substrates, which increases adhesion by up to 100x, improving the integration of these materials with rigid electronics. It is shown that the fracture energy and thermal conductivity of these materials can be tuned by controlling the size and volume loading of the LM inclusions. The utility of this method is then shown through the permanent bonding of LM composites to rigid electronics for use as thermal interface materials. \\ Chapter 4 introduces a multi-component shape morphing material that leverages an LMPA endoskeleton and soft LM resistive heaters to produce rapid (< 0.1 s) and reversible shape change. The morphing material utilizes a unique 'reversible plasticity' mechanism enabled by patterned kirigami cuts that allows for instantaneous shape fixing into load bearing shapes without the need for sustained power. The material properties are enabling for the creation of shape morphing robots, which we show through by integration of on board power and control to create a multi-modal morphing drone capable of land and air transport as well as through an underwater machine that can be reversibly deployed to obtain cargo. For magnetic elastomers, the magneto-mechanical properties of state-of-the-art magnetorheological elastomers (MREs) with diverse structures are studied. These materials have long been studied for their ability to rapidly tune stiffness in the presence of a magnetic field. Chapter 5 introduces a new form of hybrid MRE material architecture which utilizes a combination of magnetic powders and fluids to achieve high magnetic permeability and low stiffness for wearable electronic applications. The zero-field magneto-mechanical properties of MREs with rigid particles, magnetic fluids, and a combination of the two are studied. The inclusions are modeled through an Eshelby analysis which demonstrates magnetic fluids can be utilized to increase magnetic response while decreasing the stiffness of the composite material. The stiffness tuning capabilities of these material architectures are then explored in Chapter 6, where we introduce a predictive model that captures the stiffness tuning response of MREs across diverse microstructures and compositions. This model guides the creation of materials with rapid (~ 20 ms) and extreme stiffness tuning (70x) which we utilize to create a soft adaptive gripper capable of handling objects of diverse geometries. / Doctor of Philosophy / Multi-component soft materials offer innovative solutions for traditional and emerging technologies by possessing unique combinations of tunable functionality and adaptive mechanical properties. These materials often incorporate functional inclusions such as metals or ceramics in elastomers in order to create deformable composite structures with high thermal or electrical conductivities, magnetic material response, or user-controlled shape morphing and stiffness change. In recent years, these materials have become enabling for wearable electronics and soft machines which has led to the development of new materials that provide advanced functionalities while maintaining a low stiffness and high extensibility. In this work, we develop methods for the fabrication and utilization of advanced materials that integrate room temperature liquid metals (LM), low melting point alloys (LMPA), and magnetic powders and fluids with soft elastomers to introduce multifunctionality to electronic and machine systems. LM-elastomer composites which have high thermal and electrical conductivities are enabling for heat transfer and stretchable electronic applications for wearable electronics and soft robots. These materials have been utilized to create emerging devices such as electronics that are capable of improving human health and efficiency, as well as robots capable of adapting their functions based on environmental need. One possible area where LM composites could be applied is in marine environments, where wearable electronics can improve safety for divers, and soft robots could be utilized for underwater exploration. In Chapter 2, we provide the first study to quantify the effects of underwater aging in freshwater and saltwater environments on the important mechanical and functional properties of LM composites for long-term underwater use. It is found that LM composites are largely resistant to changes in their mechanical properties, as well as both thermal and electrical functionality due to long-term underwater aging. In Chapter 3, we introduce a new chemical approach for the tough bonding of LM composites to diverse substrates, which increases adhesion by up to 100x, improving the integration of these materials with rigid electronics. It is shown that the adhesion and thermal conductivity of these materials can be tuned by controlling the size and volume loading of the LM inclusions. The utility of this method is then shown through the permanent bonding of LM composites to rigid electronics for use as thermal interface materials. Chapter 4 introduces a multi-component shape morphing material that leverages an LMPA endoskeleton and soft LM resistive heaters to produce rapid (< 0.1 s) and reversible shape change. The morphing material utilizes a unique 'reversible plasticity' mechanism enabled by patterned kirigami cuts that allows for instantaneous shape fixing into load bearing shapes without the need for sustained power. The material properties are enabling for the creation of shape morphing robots, which we show through by integration of on board power and control to create a multi-modal morphing drone capable of land and air transport as well as through an underwater machine that can be reversibly deployed to obtain cargo. For magnetic elastomers, the magnetic and mechanical properties of state-of-the-art magnetorheological elastomers (MREs) with diverse structures are studied. These materials have long been studied for their ability to rapidly change stiffness in the presence of a magnetic field. Chapter 5 introduces a new form of hybrid MRE material architecture which utilizes a combination of magnetic powders and fluids to achieve exceptional magnetic properties and low stiffness for wearable electronic applications. The mechanical properties of MREs with rigid particles, magnetic fluids, and a combination of the two are studied. The inclusions are modeled through a mechanical analysis which demonstrates magnetic fluids can be utilized to increase magnetic character while decreasing the stiffness of the composite material. The stiffness tuning capabilities of these material architectures are then explored in Chapter 6, where we introduce a predictive model that captures the stiffness tuning response of MREs across diverse microstructures and compositions. This model guides the creation of materials with rapid (~ 20 ms) and extreme stiffness tuning (70x) which we utilize to create a soft adaptive gripper capable of handling objects of diverse geometries.